earth round trip distance

Earth – our home planet – is the third planet from the Sun, and the fifth largest planet. It's the only place we know of inhabited by living things.

Quick Facts

Length of Day

Length of year.

365.25 days

Distance from Sun

93,327,712 miles / 150,196,428 kilometers

One Way Light Time to Sun

8.350022 minutes

While Earth is only the fifth largest planet in the solar system, it is the only world in our solar system with liquid water on the surface. Just slightly larger than nearby Venus, Earth is the biggest of the four planets closest to the Sun, all of which are made of rock and metal.

Earth is the only planet in the solar system whose English name does not come from Greek or Roman mythology. The name was taken from Old English and Germanic. It simply means "the ground." There are, of course, many names for our planet in the thousands of languages spoken by the people of the third planet from the Sun.

The name Earth is at least 1,000 years old. All of the planets, except for Earth, were named after Greek and Roman gods and goddesses. However, the name Earth is a Germanic word, which simply means “the ground.”

Potential for Life

Earth has a very hospitable temperature and mix of chemicals that have made life abundant here. Most notably, Earth is unique in that most of our planet is covered in liquid water, since the temperature allows liquid water to exist for extended periods of time. Earth's vast oceans provided a convenient place for life to begin about 3.8 billion years ago.

Some of the features of our planet that make it great for sustaining life are changing due to the ongoing effects of climate change .

Size and Distance

With an equatorial diameter of 7926 miles (12,760 kilometers), Earth is the biggest of the terrestrial planets and the fifth largest planet in our solar system.

From an average distance of 93 million miles (150 million kilometers), Earth is exactly one astronomical unit away from the Sun because one astronomical unit (abbreviated as AU), is the distance from the Sun to Earth. This unit provides an easy way to quickly compare planets' distances from the Sun.

It takes about eight minutes for light from the Sun to reach our planet.

Orbit and Rotation

As Earth orbits the Sun, it completes one rotation every 23.9 hours. It takes 365.25 days to complete one trip around the Sun. That extra quarter of a day presents a challenge to our calendar system, which counts one year as 365 days. To keep our yearly calendars consistent with our orbit around the Sun, every four years we add one day. That day is called a leap day, and the year it's added to is called a leap year.

Earth's axis of rotation is tilted 23.4 degrees with respect to the plane of Earth's orbit around the Sun. This tilt causes our yearly cycle of seasons. During part of the year, the northern hemisphere is tilted toward the Sun, and the southern hemisphere is tilted away. With the Sun higher in the sky, solar heating is greater in the north producing summer there. Less direct solar heating produces winter in the south. Six months later, the situation is reversed. When spring and fall begin, both hemispheres receive roughly equal amounts of heat from the Sun.

Earth is the only planet that has a single moon.  Our Moon  is the brightest and most familiar object in the night sky. In many ways, the Moon is responsible for making Earth such a great home. It stabilizes our planet's wobble, which has made the climate less variable over thousands of years.

Earth sometimes temporarily hosts orbiting asteroids or large rocks. They are typically trapped by Earth's gravity for a few months or years before returning to an orbit around the Sun. Some asteroids will be in a long “dance” with Earth as both orbit the Sun.

Some moons are bits of rock that were captured by a planet's gravity, but our Moon is likely the result of a collision billions of years ago. When Earth was a young planet, a large chunk of rock smashed into it, displacing a portion of Earth's interior. The resulting chunks clumped together and formed our Moon. With a radius of 1,080 miles (1,738 kilometers), the Moon is the fifth largest moon in our solar system (after Ganymede, Titan, Callisto, and Io).

The Moon is an average of 238,855 miles (384,400 kilometers) away from Earth. That means 30 Earth-sized planets could fit in between Earth and its Moon.

Earth has no rings.

When the solar system settled into its current layout about 4.5 billion years ago, Earth formed when gravity pulled swirling gas and dust in to become the third planet from the Sun. Like its fellow terrestrial planets, Earth has a central core, a rocky mantle, and a solid crust.

Earth is composed of four main layers, starting with an inner core at the planet's center, enveloped by the outer core, mantle, and crust.

The inner core is a solid sphere made of iron and nickel metals about 759 miles (1,221 kilometers) in radius. There the temperature is as high as 9,800 degrees Fahrenheit (5,400 degrees Celsius). Surrounding the inner core is the outer core. This layer is about 1,400 miles (2,300 kilometers) thick, made of iron and nickel fluids.

In between the outer core and crust is the mantle, the thickest layer. This hot, viscous mixture of molten rock is about 1,800 miles (2,900 kilometers) thick and has the consistency of caramel. The outermost layer, Earth's crust, goes about 19 miles (30 kilometers) deep on average on land. At the bottom of the ocean, the crust is thinner and extends about 3 miles (5 kilometers) from the seafloor to the top of the mantle.

Like Mars and Venus, Earth has volcanoes, mountains, and valleys. Earth's lithosphere, which includes the crust (both continental and oceanic) and the upper mantle, is divided into huge plates that are constantly moving. For example, the North American plate moves west over the Pacific Ocean basin, roughly at a rate equal to the growth of our fingernails. Earthquakes result when plates grind past one another, ride up over one another, collide to make mountains, or split and separate.

Earth's global ocean, which covers nearly 70% of the planet's surface, has an average depth of about 2.5 miles (4 kilometers) and contains 97% of Earth's water. Almost all of Earth's volcanoes are hidden under these oceans. Hawaii's Mauna Kea volcano is taller from base to summit than Mount Everest, but most of it is underwater. Earth's longest mountain range is also underwater, at the bottom of the Arctic and Atlantic oceans. It is four times longer than the Andes, Rockies and Himalayas combined.

Near the surface, Earth has an atmosphere that consists of 78% nitrogen, 21% oxygen, and 1% other gases such as argon, carbon dioxide, and neon. The atmosphere affects Earth's long-term climate and short-term local weather and shields us from much of the harmful radiation coming from the Sun. It also protects us from meteoroids, most of which burn up in the atmosphere, seen as meteors in the night sky, before they can strike the surface as meteorites.

Magnetosphere

Our planet's rapid rotation and molten nickel-iron core give rise to a magnetic field, which the solar wind distorts into a teardrop shape in space. (The solar wind is a stream of charged particles continuously ejected from the Sun.) When charged particles from the solar wind become trapped in Earth's magnetic field, they collide with air molecules above our planet's magnetic poles. These air molecules then begin to glow and cause aurorae, or the northern and southern lights.

The magnetic field is what causes compass needles to point to the North Pole regardless of which way you turn. But the magnetic polarity of Earth can change, flipping the direction of the magnetic field. The geologic record tells scientists that a magnetic reversal takes place about every 400,000 years on average, but the timing is very irregular. As far as we know, such a magnetic reversal doesn't cause any harm to life on Earth, and a reversal is very unlikely to happen for at least another thousand years. But when it does happen, compass needles are likely to point in many different directions for a few centuries while the switch is being made. And after the switch is completed, they will all point south instead of north.

8 Need-to-Know Things About Our Home Planet

• Measuring Up - If the Sun were as tall as a typical front door, Earth would be the size of a nickel.
• We're On It - Earth is a rocky planet with a solid and dynamic surface of mountains, canyons, plains and more. Most of our planet is covered in water.
• Breathe Easy - Earth's atmosphere is 78 percent nitrogen, 21 percent oxygen and 1 percent other ingredients—the perfect balance to breathe and live.
• Our Cosmic Companion - Earth has one moon.
• Ringless - Earth has no rings.
• Orbital Science - Many orbiting spacecraft study the Earth from above as a whole system—observing the atmosphere, ocean, glaciers, and the solid earth.
• Home, Sweet Home - Earth is the perfect place for life as we know it.
• Protective Shield - Our atmosphere protects us from incoming meteoroids, most of which break up in our atmosphere before they can strike the surface.

Kid-Friendly Earth

Our home planet Earth is a rocky, terrestrial planet. It has a solid and active surface with mountains, valleys, canyons, plains and so much more. Earth is special because it is an ocean planet. Water covers 70% of Earth's surface. Earth's atmosphere is made mostly of nitrogen and has plenty of oxygen for us to breathe. The atmosphere also protects us from incoming meteoroids, most of which break up before they can hit the surface.

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How many miles around the Earth?

Earth is the fifth largest planet in the Solar System and the third planet from the Sun. It is the biggest terrestrial planet. But how big is it? If a person would walk from one end to the other, how many miles around the Earth would that person walk? The short answer is around 24.901 miles.

The mean radius of Earth is at around 3.958 mi / 6.371 km, slightly larger than Venus , almost twice the radius of Mars and about three times that of Mercury.

If you started walking from one end to the other, you would have to cover more than 24.901 mi / 40.075 km. However, things are more complicated than this since Earth is not a perfect sphere.

The Shape of the Earth

Earth is a flattened sphere; it has an oblate spheroid shape. The Earth is flattened along its axis from pole to pole resulting in a bulge at the equator.

This bulge comes from Earth’s rotation, which causes the diameter at the equator to be 27 mi / 43 km larger than the pole-to-pole diameter. Depending on where a person traveled from, they would ultimately traverse a different amount of miles – kilometers.

Humanity has viewed Earth as spherical since the ancient Greeks. Pythagoras is mostly credited for being the first to suggest this in the 6 th   century BCE.

Not much is known about how classical scholars came to this conclusion. Some believe that it all started when the travel and trade between the Greek settlements led to variations in the observable latitude and the change in the area of circumpolar stars.

Specific starts that were visible in Egypt and Cyprus were not visible in northern latitudes, such as Crimea. These variations were noticeable, especially to navigators who often relied on these stars .

Since these distant objects disappeared beneath the horizon, it may have led to some people concluding that the Earth’s surface is curved. By 240 BCE, the Greek astronomer Eratosthenes estimated the Earth’s circumference.

He measured the angles of the shadows cast by the Sun , and using different aspects to perform trigonometric calculations; he calculated the circumference to within a 2-20% margin of error.

Since Eratosthenes did this, the topic became a scientific matter. Later, in the 17 th century, with the advancement of technology, the idea of a perfectly spherical Earth was slowly abandoned.

Sir Isaac Newton was the first to suggest this, and he started to propose that Earth’s equator had to be wider than its poles. During the advent of the Space Age and the ability to use orbital satellites to measure the planet from space, this was finally confirmed.

Equatorial – Meridional

The flattened spherical nature of Earth is reflected in terms of its equatorial and meridional circumference. At the equator, Earth has a circumference of 24.901.461 mi / 40.075.017 km.

When it comes to measurements from pole-to-pole, or along the meridian line, the Earth has a circumference of 24.859.73 mi / 40.007.86 km.

This is also reflected in Earth’s radius, which differs depending on which latitude it is measured at. If you measured the radius from Earth’s center to the equator, you would obtain a radius of 3.963.2 mi / 6.378.1 km.

However, if you would measure it from the center to one of Earth’s polar regions, you would obtain a radius of 3.949.9 mi / 6.356.8 km. It isn’t such a big difference, but it is present.

Many scientists have continued to develop several other models that represent the closest approximation of the shape of the Earth. However, for the most part, it is described as a sphere. But why do some people believe that the Earth is flat?

Flat Earth Theory

Often described as the ultimate conspiracy theory, a group of people argues that the Earth’s shape is flat. Their arguments are often pretty simplistic, such as:

• Walking on Earth looks/feels flat
• Any scientific evidence is fabricated/orchestrated by NASA and/or the government agencies

The theory states that Earth is a disc with the Arctic Circle in the center and Antarctica, a 150-foot-tall wall of ice, around the rim. Scientists from NASA are supposedly guarding this wall.

There are many other theories within this one, trying to explain gravity or the movements of the Sun and Moon . It is quite extraordinary that some people believed this.

However, there is one thing to keep in mind. Many, if not most, flat-Earthers are merely lying about their belief simply out of fun, profit, or general disinformation.

Though the number of flat-Earthners is small, their overall existence, for some people, is enough to deter their belief upon the shape of the Earth.

Did you know?

• The name “Earth” is at least 1.000 years old. It is a Germanic word that translates to “the ground.” No one knows who came up with it; however, Earth is the only planet that doesn’t bear a Greek or Roman deity name.
• Earth is 91 million mi / 147 million km away from the Sun or 1 AU.
• If Earth’s crustal surface would be at the same elevation, the depth of the oceans would only be at 1.68 mi / 2.7 km.
• How fast does the Moon orbit the Earth? Well, it is the equivalent of a rifle bullet.
• We are traveling through space on this big rock called home, at around 67.000 mi / 107.826 km per hour. However, when it comes to Earth’s rotation, it is slowing down at about 17 milliseconds every 1.000 years or so. This slowing down process is due to the Moon’s presence.
• Earth’s continents move at the same rate as how fast human fingernails grow.
• Universetoday

Image sources:

• https://solarsystem.nasa.gov/system/stellar_items/image_files/4_earth.jpg
• https://www.universetoday.com/wp-content/uploads/2014/04/800px-Size_planets_comparison.jpg
• https://cdn.britannica.com/19/129119-050-6ED737BC/World-map-red-line-Equator.jpg
• https://images.ctfassets.net/cnu0m8re1exe/3WJ0dJy4VIbegdvdcdfikb/62382fdcb2519b3672a0b4e8d4dbacff/Screen-Shot-2018-11-26-at-1.58.03-PM.png?w=650&h=433&fit=fill
• https://d.newsweek.com/en/full/1508883/flat-earth-soccor.jpg

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ENCYCLOPEDIC ENTRY

Earth is the planet we live on, the third of eight planets in our solar system and the only known place in the universe to support life.

Earth Science, Astronomy, Geology, Geography, Physical Geography

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Learning materials.

• The active outer shell of Earth is dominated by tectonic plates, whose interactions result in volcanic eruptions, earthquakes, and geysers. Click to visit MapMaker Interactive's layer on Earth's tectonic plates.

Earth is the planet we live on, one of eight planets in our solar system and the only known place in the universe to support life.

Earth is the third planet from the sun , after Mercury and Venus, and before Mars. It is about 150 million kilometers (about 93 million miles) from the sun. This distance, called an astronomical unit (AU), is a standard unit of measurement in astronomy . Earth is one AU from the sun. The planet Jupiter is about 5.2 AU from the sun—about 778 million kilometers (483.5 million miles).

Earth is the largest and most massive of the rocky inner planets , although it is dwarfed by the gas giants beyond the Asteroid Belt . Its diameter is about 12,700 kilometers (7,900 miles), and its mass is about 5.97×1024 kilograms (6.58×1021 tons). In contrast, Jupiter, the largest planet in the solar system, has a diameter of 143,000 kilometers (88,850 miles), and its mass is about 1,898×1024 kilograms (2093×1021 tons).

Earth is an oblate spheroid . This means it is spherical in shape, but not perfectly round. It has a slightly greater radius at the Equator , the imaginary line running horizontally around the middle of the planet. In addition to bulging in the middle, Earth’s poles are slightly flattened. The geoid describes the model shape of Earth, and is used to calculate precise surface locations.

Earth has one natural satellite , the moon . Earth is the only planet in the solar system to have one moon. Venus and Mercury do not have any moons, for example, while Jupiter and Saturn each have more than a dozen.

Planet Earth  

Earth’s interior is a complex structure of superheated rocks. Most geologists recognize three major layers: the dense core , the bulky mantle , and the brittle crust . No one has ever ventured below Earth’s crust.

Earth’s core is mostly made of iron and nickel . It consists of a solid center surrounded by an outer layer of liquid . The core is found about 2,900 kilometers (1,802 miles) below Earth’s surface, and has a radius of about 3,485 kilometers (2,165 miles).

A mantle of heavy rock (mostly silicates ) surrounds the core. The mantle is about 2,900 kilometers (1,802 miles) thick, and makes up a whopping 84 percent of Earth’s total volume . Parts of the mantle are molten , meaning they are composed of partly melted rock. The mantle’s molten rock is constantly in motion. It is forced to the surface during volcanic eruptions and at mid-ocean ridges .

Earth’s crust is the planet’s thinnest layer, accounting for just one percent of Earth’s mass. There are two kinds of crust: thin, dense oceanic crust and thick, less-dense continental crust . Oceanic crust extends about five to 10 kilometers (three to six miles) beneath the ocean floor. Continental crust is about 35 to 70 kilometers (22 to 44 miles) thick.

Exterior: Tectonic Activity

The crust is covered by a series of constantly moving tectonic plates . New crust is created along mid-ocean ridges and rift valleys , where plates pull apart from each other in a process called rifting . Plates slide above and below each other in a process called subduction . They crash against each other in a process called faulting .

Tectonic activity such as subduction and faulting has shaped the crust into a variety of landscapes . Earth’s highest point is Mount Everest, Nepal, which soars 8,850 kilometers (29,035 feet) in the Himalaya Mountains in Asia. Mount Everest continues to grow every year, as subduction drives the Indo-Australian tectonic plate below the Eurasian tectonic plate. Subduction also creates Earth’s deepest point, the Mariana Trench, about 11 kilometers (6.9 miles) below the surface of the Pacific Ocean. The heavy Pacific plate is being subducted beneath the small Mariana plate.

Plate tectonics are also responsible for landforms such as geysers , earthquakes , and volcanoes . Tectonic activity around the Pacific plate, for instance, creates the Ring of Fire . This tectonically active area includes volcanoes such as Mount Fuji, Japan, and earthquake-prone fault zones such as the west coast of the United States.

Revolution and Rotation

Earth is a rocky body constantly moving around the sun in a path called an orbit . Earth and the moon follow a slightly oval-shaped orbit around the sun every year.

Each journey around the sun, a trip of about 940 million kilometers (584 million miles), is called a revolution. A year on Earth is the time it takes to complete one revolution, about 365.25 days. Earth orbits the sun at a speedy rate of about 30 kilometers per second (18.5 miles per second).

At the same time that it revolves around the sun, Earth rotates on its own axis . Rotation is when an object, such as a planet, turns around an invisible line running down its center. Earth’s axis is vertical, running from the North Pole to the South Pole. Earth makes one complete rotation about every 24 hours. Earth rotates unevenly, spinning faster at the Equator than at the poles. At the Equator, Earth rotates at about 1,670 kilometers per hour (1,040 miles per hour), while at 45° north, for example, (the approximate latitude of Green Bay, Wisconsin, United States) Earth rotates at 1,180 kilometers per hour (733 miles per hour).

Earth’s rotation causes the periods of light and darkness we call day and night. The part of Earth facing the sun is in daylight; the part facing away from the sun is in darkness. If Earth did not rotate, one-half of Earth would always be too hot to support life, and the other half would be frozen. Earth rotates from west to east, so the sun appears to rise in the east and set in the west. 

In addition to Earth’s revolution and rotation periods, we experience light and darkness due to Earth’s axis not being straight up-and-down. Earth’s axis of rotation is tilted 23.5°. This tilt influences temperature changes and other weather patterns from season to season. 

The Spheres

Earth’s physical environment is often described in terms of spheres: the magnetosphere , the atmosphere , the hydrosphere , and the lithosphere . Parts of these spheres make up the biosphere , the area of Earth where life exists.

Magnetosphere

Earth’s magnetosphere describes the pocket of space surrounding our planet where charged particles are controlled by Earth’s magnetic field .

The charged particles that int eract with Earth’s magnetosphere are called the solar wind . The pressure of the solar wind compresses the magnetosphere on the “dayside” of Earth to about 10 Earth radii. The long tail of the magnetosphere on the “nightside” of Earth stretches to hundreds of Earth radii. The most well-known aspect of the magnetosphere are the charged particles that sometimes interact over its poles—the auroras , or Northern and Southern Lights.

Earth’s atmosphere is a blanket of gases enveloping Earth and retained by our planet’s gravity . Atmospheric gases include nitrogen, water vapor , oxygen , and carbon dioxide .

The atmosphere is responsible for temperature and other weather patterns on Earth. It blocks most of the sun’s ultraviolet radiation (UV), conducts solar radiation and precipitation through constantly moving air masses , and keeps our planet’s average surface temperature to about 15° Celsius (59° Fahrenheit).

The atmosphere has a layered structure. From the ground toward the sky, the layers are the troposphere , stratosphere , mesosphere , thermosphere , and exosphere . Up to 75 percent of the total mass of the atmosphere is in the troposphere, where most weather occurs. The boundaries between the layers are not clearly defined, and change depending on latitude and season.

Hydrosphere

The hydrosphere is composed of all the water on Earth. Nearly three-fourths of Earth is covered in water, most of it in the ocean. Less than three percent of the hydrosphere is made up of freshwater . Most freshwater is frozen in ice sheets and glaciers in Antarctica, the North American island of Greenland, and the Arctic. Freshwater can also be found underground, in chambers called aquifers , as well as rivers , lakes , and springs .

Water also circulates around the world as vapor. Water vapor can condense into clouds and fall back to Earth as precipitation.

The hydrosphere helps regulate Earth’s temperature and climate . The ocean absorbs heat from the sun and interacts with the atmosphere to move it around Earth in air currents .

Lithosphere

The lithosphere is Earth’s solid shell. The crust and the upper portion of the mantle form the lithosphere. It extends from Earth’s surface to between 50 and 280 kilometers (31 to 174 miles) below it. The difference in thickness accounts for both thin oceanic and thicker continental crust.

The rocks and minerals in Earth’s lithosphere are made of many elements . Rocks with oxygen and silicon , the most abundant elements in the lithosphere, are called silicates. Quartz is the most common silicate in the lithosphere—and the most common type of rock on Earth.

Cycles on Earth

Almost all materials on Earth are constantly being recycled . The three most common cycles are the water cycle , the carbon cycle , and the rock cycle .

Water Cycle

The water cycle involves three main phases, related to the three states of water: solid, liquid, and gas. Ice , or solid water, is most common near the poles and at high altitudes . Ice sheets and glaciers hold the most solid water.

Ice sheets and glaciers melt, transforming into liquid water. The most abundant liquid water on the planet is in the ocean, although lakes, rivers, and underground aquifers also hold liquid water. Life on Earth is dependent on a supply of liquid water. Most organisms, in fact, are made up mostly of liquid water, called body water . The human body is about 50 percent to 60 percent body water. In addition to survival and hygiene , people use liquid water for energy and transportation .

The third phase of the water cycle occurs as liquid water evaporates. Evaporation is the process of a liquid turning into a gas, or vapor. Water vapor is invisible and makes up part of the atmosphere. As water vapor condenses, or turns back into liquid, pockets of vapor become visible as clouds and fog . Eventually, clouds and fog become saturated , or full of liquid water. This liquid water falls to Earth as precipitation. It can then enter a body of water, such as an ocean or lake, or freeze and become part of a glacier or ice sheet. The water cycle starts again.

Carbon Cycle

The carbon cycle involves the exchange of the element carbon through Earth’s atmosphere, hydrosphere, and lithosphere. Carbon, essential for all life on Earth, enters the biosphere many ways. Carbon is one of the gases that make up the atmosphere. It is also ejected during the eruption of volcanoes and ocean vents .

All living or once-living materials contain carbon. These materials are organic . Plants and other autotrophs depend on carbon dioxide to create nutrients in a process called photosynthesis . These nutrients contain carbon. Animals and other organisms that consume autotrophs obtain carbon. Fossil fuels , the remains of ancient plants and animals, contain very high amounts of carbon.

As organisms die and decompose , they release carbon into the ocean, soil , or atmosphere. Plants and other autotrophs use this carbon for photosynthesis, starting the carbon cycle again.

The rock cycle is a process that explains the relationship between the three main types of rocks: igneous, sedimentary, and metamorphic. Unlike water in the water cycle and or carbon in the carbon cycle, not all rocks are recycled in different forms. There are some rocks that have been in their present form since soon after Earth cooled. These stable rock formations are called cratons .

Igneous rocks are formed as lava hardens. Lava is molten rock ejected by volcanoes during eruptions. Granite and basalt are common types of igneous rocks. Igneous rocks can be broken apart by the forces of erosion and weathering . Winds or ocean currents may then transport these tiny rocks ( sand and dust ) to a different location.

Sedimentary rocks are created from millions of tiny particles slowly building up over time. Igneous rocks can become sedimentary by collecting with other rocks into layers. Sedimentary rocks include sandstone and limestone .

Metamorphic rocks are formed when rocks are subjected to intense heat and pressure. The rocks change (undergo metamorphosis ) to become a new type of rock. Marble , for example, is a metamorphic rock created from rock that was once limestone, a sedimentary rock.

Earth’s Evolution

Earth and the rest of the solar system formed about 4.6 billion years ago from a huge, spinning cloud of gas and dust.

Over a period of about 10 million years, the dense center of the cloud grew very hot. This massive center became the sun. The rest of the particles and objects continued to revolve around the sun, colliding with each other in clumps. Eventually, these clumps compressed into planets, asteroids , and moons. This process generated a lot of heat. 

Eventually, Earth began to cool and its materials began to separate. Lighter materials floated upward and formed a thin crust. Heavier materials sank toward Earth’s center. Eventually, three main layers formed: the core, the mantle, and the crust.

As Earth’s internal structure developed, gases released from the interior mixed together, forming a thick, steamy atmosphere around the planet. Water vapor condensed, and was augmented by water from asteroids and comets that continued to crash to Earth. Rain began to fall and liquid water slowly filled basins in Earth’s crust, forming a primitive ocean that covered most of the planet. Today, ocean waters continue to cover nearly three-quarters of our planet.

The end of Earth will come with the end of the sun. In a few billion years, the sun will no longer be able to sustain the nuclear reactions that keep its mass and luminosity consistent . First, the sun will lose more than a quarter of its mass, which will loosen its gravitational hold on Earth. Earth’s orbit will widen to about 1.7 AU. But the sun will also gain volume, expanding to about 250 times its current size. The sun in this red giant phase will drag Earth into its own fiery atmosphere, destroying the planet.

Eras on Earth

Paleontologists , geologists, and other scientists divide Earth’s history into time periods. The largest time period is the supereon , and only applies to one unit of time, the Precambrian . Eons , eras, and periods are smaller units of geologic time.

Most of Earth’s history took place in the Pre cambrian , which began when Earth was cooling and ended about 542 million years ago. Life began in the Precambrian, in the forms of bacteria and other single-celled organisms. Fossils from the Precambrian are rare and difficult to study. The Precambrian supereon is usually broken into three eons: the Hadean , the Archaean , and the Proterozoic .

We are currently living in the Phanerozoic eon.

The first major era of the Phanerozoic is called the Paleozoic, and the Cambrian is the first period of the Paleozoic era . “The Cambrian Explosion of Life ” was the rapid appearance of almost all forms of life. Paleontologists and geologists have studied fossils of archaea , bacteria, algae , fungi , plants, and animals that lived during the Cambrian period. The Cambrian was followed by the Ordovician, Silurian, Devonian, Carboniferous, and Permian periods.

The Mesozoic era began about 251 million years ago. This was the era when dinosaurs flourished . The Mezozoic has three periods: the Triassic, the Jurassic, and the Cretaceous.

We currently live in the Cenozoic era, which began about 65 million years ago. The Cenozoic is generally marked by three periods: the Paleogene, the Neogene, and the Quaternary . We live in the Quaternary period, which began about 2.5 million years ago. All ancestors of Homo sapiens (modern humans) evolved during the Quaternary.

Earth by the Numbers

Surface Gravity: 1 (one kilogram on Earth)

Orbital Period: 365.256 days

Satellites: 1 (the Moon)

Atmosphere: nitrogen (78%), oxygen (21%), argon, carbon dioxide, neon

Average Temperature: 15° Celsius (77 Kelvin, 59° Fahrenheit)

Ingredients for Life Scientists have gathered enough information about other planets in our solar system to know that none can support life as we know it. Life is not possible without a stable atmosphere containing the right chemical ingredients for living organisms: hydrogen, oxygen, nitrogen, and carbon. These ingredients must be balanced—not too thick or too thin. Life also depends on the presence of water. Jupiter, Saturn, Uranus, and Neptune all have atmospheres made mostly of hydrogen and helium. These planets are called gas giants, because they are mostly made of gas and do not have a solid outer crust. Mercury and Mars have some of the right ingredients, but their atmospheres are far too thin to support life. The atmosphere of Venus is too thick—the planet's surface temperature is more than 460 degrees Celsius (860 degrees Fahrenheit). Jupiter's moon Europa has a thin atmosphere rich with oxygen. It is likely covered by a huge ocean of liquid water. Some astrobiologists think that if life exists elsewhere in the solar system, it will be near vents at the bottom of Europa's ocean.

Earth to Earth Earth is the only planet in the solar system not named for a Greek or Roman deity. "Earth" originally meant the soil and land of our planet. (This is still what it means when the word is lowercase.) Eventually, Earth came to mean the planet itself.

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October 19, 2023

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November 24, 2014

Earth's orbit around the sun

by Matt Williams, Universe Today

Ever since the 16th century when Nicolaus Copernicus demonstrated that the Earth revolved around in the Sun, scientists have worked tirelessly to understand the relationship in mathematical terms. If this bright celestial body – upon which depends the seasons, the diurnal cycle, and all life on Earth – does not revolve around us, then what exactly is the nature of our orbit around it?

For several centuries, astronomers have applied the scientific method to answer this question, and have determined that the Earth's orbit around the Sun has many fascinating characteristics.

First of all, the speed of the Earth's orbit around the Sun is 108,000 km/h, which means that our planet travels 940 million km during a single orbit. The Earth completes one orbit every 365.242199 mean solar days, a fact which goes a long way towards explaining why need an extra calendar day every four years (aka. during a leap year).

The planet's distance from the Sun also varies as it orbits. In fact, the Earth is never the same distance from the Sun from day to day. When the Earth is closest to the Sun, it is said to be at perihelion. This occurs around January 3rd each year, when the Earth is at a distance of about 147,098,074 km. When it is at its farthest distance from the Sun, Earth is said to be at aphelion – which happens around July 4th where the Earth reaches a distance of about 152,097,701 km. And those of you in the northern hemisphere will notice that "warm" or "cold" weather does not coincide with how close the Earth is to the Sun. That is determined by axial tilt, which we discuss below.

The average distance of the Earth from the aun is about 149.6 million km, which is also referred to as one astronomical unit (AU).

Next, there is the nature of the Earth's orbit. Rather than being a perfect circle, the Earth moves around the Sun in an extended circular or oval pattern. This is what is known as an "elliptical" orbit. This orbital pattern was first described by Johannes Kepler, a German mathematician and astronomer, in his seminal work Astronomia nova (New Astronomy).

After measuring the orbits of the Earth and Mars, he noticed that at times, the orbits of both planets appeared to be speeding up or slowing down. This coincided directly with the planets' aphelion and perihelion, meaning that the planets' distance from the Sun bore a direct relationship to the speed of their orbits. It also meant that both Earth and Mars did not orbit the Sun in perfectly circular patterns.

In describing the nature of elliptical orbits, scientists use a factor known as "eccentricity", which is expressed in the form of a number between zero and one. If a planet's eccentricity is close to zero, then the ellipse is nearly a circle. If it is close to one, the ellipse is long and slender.

Earth's orbit has an eccentricity of less than 0.02, which means that it is very close to being circular. That is why the difference between the Earth's distance from the Sun at perihelion and aphelion is very little – less than 5 million km.

Third, there is the role Earth's orbit plays in the seasons, which we referred to above. The four seasons are determined by the fact that the Earth is tilted 23.4° on its vertical axis, which is referred to as "axial tilt." This quirk in our orbit determines the solstices – the point in the orbit of maximum axial tilt toward or away from the Sun – and the equinoxes, when the direction of the tilt and the direction to the Sun are perpendicular.

In short, when the northern hemisphere is tilted away from the Sun, it experiences winter while the southern hemisphere experiences summer. Six months later, when the northern hemisphere is tilted towards the Sun, the seasonal order is reversed.

In the northern hemisphere, winter solstice occurs around December 21st, summer solstice is near June 21st, spring equinox is around March 20th and autumnal equinox is about September 23rd. The axial tilt in the southern hemisphere is exactly the opposite of the direction in the northern hemisphere. Thus the seasonal effects in the south are reversed.

While it is true that Earth does have a perihelion, or point at which it is closest to the sun , and an aphelion, its farthest point from the Sun, the difference between these distances is too minimal to have any significant impact on the Earth's seasons and climate.

Another interesting characteristic of the Earth's orbit around the Sun has to do with Lagrange Points. These are the five positions in Earth's orbital configuration around the Sun where the combined gravitational pull of the Earth and the Sun provides precisely the centripetal force required to orbit with them.

The five Lagrange Points between the Earth are labelled (somewhat unimaginatively) L1 to L5. L1, L2, and L3 sit along a straight line that goes through the Earth and Sun. L1 sits between them, L3 is on the opposite side of the Sun from the Earth, and L2 is on the opposite side of the Earth from L1. These three Lagrange points are unstable, which means that a satellite placed at any one of them will move off course if disturbed in the slightest.

The L4 and L5 points lie at the tips of the two equilateral triangles where the Sun and Earth constitute the two lower points. These points liem along Earth's orbit, with L4 60° behind it and L5 60° ahead. These two Lagrange Points are stable, hence why they are popular destinations for satellites and space telescopes.

The study of Earth's orbit around the Sun has taught scientists much about other planets as well. Knowing where a planet sits in relation to its parent star, its orbital period, its axial tilt , and a host of other factors are all central to determining whether or not life may exist on one, and whether or not human beings could one day live there.

We have many more articles about the Earth's orbit , including 10 interesting facts about Earth. To learn more, check out this article on elliptical orbitsor check out NASA's Earth: Overview. Astronomy Cast also has a good episode on the subject entitled "Black black holes, Unbalancing the Earth, and Space Pollution."

Provided by Universe Today

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Here's what you need to know to plan a trip around the world

Dec 29, 2021 • 7 min read

Don't start planning your round-the-world trip without reading this guide © Getty Images

In 1924, a team of aviators from the USA successfully completed the first-ever circumnavigation of the globe by airplane, a feat that took 175 days, 76 stops, a cache of 15 Liberty engines, 14 spare pontoons, four aircraft and two sets of new wings. This achievement ushered in an era of international air travel, and nearly a century later, travelers are still creating their own round-the-world itineraries. 

You might not have the same worries as those early aviators, but planning a round-the-world trip has never been a more complex process. As COVID-19 continues to alter world travel , heading out on a multi-country trip might be more complicated than it has been in decades. While it might not be the right time to hit the road, luckily it's never too early to start figuring out the logistics of a trip around the globe. After all, who doesn't have a lot of pent-up wanderlust at the moment? 

When it comes to booking your trip, there are several options for booking your airfare, as well as flexibility on timing, destinations and budget. But don't let that overwhelm you – start here with our handy guide on how to plan that round-the-world trip you’ve always dreamed of.

Where and how to get a round-the-world plane ticket

The most economical way to circumnavigate the globe is to buy a round-the-world (RTW) plane ticket through a single airline alliance. These are confederations of several different airlines that make it simple to maximize the number of places you can travel and pay for it all in one place or with points. There are three primary airline alliances to choose from: Star Alliance, OneWorld and Skyteam.  Star Alliance is a coalition of 26 airlines that fly to 1300 airports in 98% of the world’s countries.  OneWorld includes 14 airlines traveling to 1100 destinations in 180 territories.  Skyteam is made up of 19 airlines that serve 1000 destinations in 170 countries.  

Read more:   How to save money when you're traveling

Once you pick an airline alliance, whether because of a loyalty program you’re already a member of or because you like its terms, conditions and destination list, you can purchase a single RTW airline ticket made up of several legs fulfilled by that alliance’s partners. The RTW ticket rules vary between each of the airline alliances, with particulars like Star Alliance’s rule that a RTW ticket can include two to 15 stops. But there are some general principles that apply to most RTW tickets, no matter which airline group you go with. 

You typically must follow one global direction (east or west – no backtracking); you must start and finish in the same country; and you must book all your flights before departure, though you can change them later (though this could incur extra charges). Typically you have one year to get from your starting point to the finish line.

How long do I need for a round-the-world trip?

You could whip around the world in a weekend if you flew non-stop, especially with the advent of new ultra-long-haul flights that can clock in at 20 hours of flight time. However, the minimum duration of most RTW tickets is 10 days – still a breathless romp. To get the most out of your round-the-world ticket, consider stock-piling vacation days, tagging on public holidays or even arranging a sabbatical from work to take off at least two months (but ideally six months to one year). Because most airline alliances give you up to a year to use your ticket, you can maximize your purchase if you plan well.

When should I travel on a round-the-world trip?

The weather will never be ideal in all your stops, so focus on what you want to do most and research the conditions there. In general, city sightseeing can be done year-round (escape extreme heat, cold or rain in museums and cafes), but outdoor adventures are more reliant on – and enjoyable in – the right weather.

Research ahead of time if any must-see destinations or must-do activities will mean facing crowds. For example, if you’re hoping to be in Austria for the famous Salzburg Festival, you’ll want to plan ahead and book your tickets months in advance. If you’re hoping to fit a shorter thru-hike into your round-the-world trip, you’ll want to make sure you’re going in the correct season and starting in the right spot. You won’t get far or have as enjoyable an experience if you’re, say, attempting the Tour du Mont Blanc during the dates of the annual winter marathon or headed northbound on the Pacific Crest Trail in July, missing most of the warmer months. 

Accept youʼll be in some regions at the "wrong" time – though this might offer unexpected benefits. For example, Victoria Falls has a dry season each year , which means a slightly less thunderous cascade, but it does open up rafting opportunities and a chance to swim right up to the lip of the falls in The Devil’s Pool. Going to Venice in the winter might mean grayer skies but fewer crowds. Heading to Kenya and Tanzania in April is likely to mean fewer humans, but not fewer chances to spot wildlife, all while saving money on safari.  Also keep in mind that mom-and-pop locations have their downtime and holiday seasons as well; don't be too surprised if your local bakery in Paris is closed for a holiday week or two in August.

Where should I go on my round-the-world trip?

The classic (and cheapest) RTW tickets flit between a few big cities, for example, London – Bangkok – Singapore – Sydney – LA . If you want to link more offbeat hubs ( Baku – Kinshasa – Paramaribo , anyone?), prices will climb considerably. The cost of the ticket is also based on the total distance covered or the number of countries visited.

Remember, you donʼt have to fly between each point: in Australia you could land in Perth , travel overland and fly out of Cairns . Or fly into Moscow , board the Trans-Siberian railway  and fly onwards from Beijing.  Pick some personal highlights and string the rest of your itinerary around those. For instance, if youʼre a keen hiker, flesh out a Peru ( Inca Trail ) – New Zealand ( Milford Track ) – Nepal ( Everest Base Camp ) itinerary with stops in Yosemite , Menz-Gauassa and the Okavango Delta .

If budgetʼs an issue, spend more time in less expensive countries and plan budget city breaks along the way. You’ll spend more in metros like Paris, Dubai and San Francisco than in Nusa Tenggara , Budapest  and Buffalo . 

Tips, tricks and pitfalls of round-the-world tickets

Talk to an expert before you book a round-the-world ticket: you may have an itinerary in mind, but an experienced RTW flight booker will know which routes work best and cost least. A few tweaks could mean big savings in time and money. Hash out a budget well ahead of time, not only for your RTW ticket, but also for the whole trip. Reach out to friends or travel bloggers who have done a round-the-world trip or are full-time travelers because they can offer tips on how to budget for a trip around the world .

Be flexible: moving your departure date by a few days can save money. Mid-week flights are generally cheaper, as are flights on major holidays such as Christmas Day. Avoid days and times popular with business travelers to escape higher prices and more crowded cabins.

Think about internal travel: it can be cheaper to book internal flights at the same time as booking your RTW ticket, but with the global increase of low-cost airlines, you may find it better (and more flexible) to buy them separately as you go.

Be warned: if you donʼt board one of your booked flights (say, on a whim, you decide to travel overland from Bangkok to Singapore rather than fly it) your airline is likely to cancel all subsequent flights.

You might also like: 10 destinations perfect for solo travel Can visiting lesser-known places offer a better travel experience? 6 things I learned from flying 6 days in a row

This article was first published March 2012 and updated December 2021

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Fact check: Ample evidence the Earth is round and rotating, contrary to persistent social media claims

The claim: Earth isn't curved and doesn't rotate

Humans discovered the curvature and rotation of the Earth thousands of years ago, dating back to ancient Greece. Since then, scientists have only discovered more evidence to prove this is true – including seeing Earth itself from space .

But flat earth claims continue to circulate online.

"No one's seen the Earth's supposed curvature and no one has experienced the Earth's supposed rotation. BECAUSE THEY DON'T EXIST," reads a June 1 Instagram post .

This argument is used frequently in the flat Earth community, with similar claims garnering hundreds and thousands of social media interactions.

But the claim is incorrect.

People have both seen Earth's curvature and experienced Earth's rotation, experts say. 

The poster could not be reached for comment.

Follow us on Facebook!   Like our page to get updates throughout the day on our latest debunks

Rotation isn't felt because speed is constant

Most scientists estimate the Earth to be rotating around 1,000 miles per hour on its axis. 

Proof of this includes the  Coriolis force . This force explains why planes cannot simply travel in a straight line to their destination, but instead must fly along a curved route. Because the Earth rotates so rapidly, flying in a straight line would result in the plane ending up in the wrong location. The Earth is always moving, so pilots must account for how much their destination will have rotated since the start of the flight.

This effect also impacts hurricanes, which swirl counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere, said  Jason Steffen , a mathematician and physicist at the University of Nevada. If the Earth were on a flat plane, this mirroring across the equator would not occur, he said. The rotation around the Earth's access and the subsequent Coriolis forces cause these differences to occur.

The post claims the fact that this motion can't be felt by humans is evidence that the Earth is not moving. But several scientists explained the motion can't be felt because the Earth is moving at a consistent speed.

"People don’t feel motion – they feel changes in motion – accelerations," said Kevin Lee , an associate professor of physics and astronomy at the University of Nebraska. "If you are on the freeway moving at 70 mph you don’t feel that motion at all, but slam on the breaks and you definitely feel the change."

David Brown , the director of undergraduate programs at North Carolina State University's department of physics, used a similar analogy.

"When we drive down the street in a straight line at a constant speed, what we feel is the bumps in the road," he said. "Without the bumps, we would not feel the motion at all, unless the car accelerates."

It's the same reason why people don't feel like they're moving in a plane, Steffen said.

"Does that mean it's also stationary? That initial argument doesn't hold any water," he said.

The Earth is curved and humans have witnessed it

Flat earth claims are often built around the observation that the horizon appears flat from a given vantage point.

This assertion ignores  numerous examples of photographic evidence that illustrate the curvature of the Earth.

But experts also note the Earth is so large that people can't directly observe the curvature from Earth's surface. The curvature only becomes visible from a vantage point that is at least 40 miles above the Earth's surface, Steffen explained.

"You have to be about a percent or so higher than the radius of the surface of the Earth (to see the curve)," he said. "40 miles is 1% of the curvature of the radius of the Earth." Most people will not reach this altitude. However, those who have gone beyond this altitude have been able to provide photographic evidence of the curve.

Among other evidence: the North star, Polaris, would always be visible if the Earth was a level plane. However, people in the Southern Hemisphere cannot see the star at all. Watching Polaris shift positions across the sky was one of the ways the ancient Greeks first calculated the circumference of the Earth, Steffen said.

Our rating: False

Based on our research, we rate FALSE the claim that Earth isn't curved and doesn't rotate. The Earth is both, and there are several ways scientists have proved this, experts say. The curvature of the Earth can be seen from an elevated vantage point. And the rotation of the Earth also impacts daily functions like the route planes fly, it just can't be felt because humans "feel" acceleration, not speed.

Our fact-check sources:

• Kevin Lee , Nov. 7-9, Email exchange with USA TODAY
• Jason Steffen , Nov. 10, Phone call with USA TODAY
• David Brown , Nov. 7-14, Email exchange with USA TODAY
• Live Science, June 27, 2021,  How fast does the Earth move?
• National Geographic, accessed Nov. 8-14,  Horizon
• National Geographic, accessed Nov. 14,  The Coriolis Effect: Earth's Rotation and Its Effect on Weather
• Britannica, accessed Nov. 14,  Coriolis effect
• CNBC, Oct. 7, 2016,  Here's why hurricanes spin counterclockwise in the North
• The University of Nevada, March 11, 2019,  Round Earth Clues: How Science Proves that our Home is a Globe
• NASA, Dec. 24, 1968,  E arthrise
• Space, April 22, 2020,  Earth From Space: Classic NASA Photos
• CNBC, Oct. 7, 2016,  Here’s why hurricanes spin counterclockwise in the North
• SciJinks, accessed Nov. 16,  What Is the Coriolis Effect?

Thank you for supporting our journalism. You can subscribe to our print edition, ad-free app or electronic newspaper replica here.

Our fact-check work is supported in part by a grant from Faceb ook.

Earth Curvature Calculator

Accurately calculate the curvature you are supposed to see on the ball Earth.

Explanation:

The Earth's radius (r) is 6371 km or 3959 miles, based on numbers from Wikipedia , which gives a circumference (c) of c = 2 * π * r = 40 030 km

We wish to find the height (h) which is the drop in curvature over the distance (d)

Using the circumference we find that 1 kilometer has the angle 360° / 40 030 km = 0.009° . The angle (a) is then a = 0.009° * distance (d)

The derived formula h = r * (1 - cos a) is accurate for any distance (d)

Source code

Note: Using the formula 8 times the distance in miles squared is not accurate for long distances but is fine for practical use.

10 ways you can tell the Earth is round

Test the thoroughly debunked argument for yourself.

By Moriel Schottlender | Updated May 1, 2023 10:46 AM EDT

Moriel Schottlender is a software engineer at Wikimedia Foundation. This article was originally posted on her Smarter Than That blog in 2008 and has been lightly edited for Popular Science.

Humanity has known the world is not flat for a few millennia, and I’ve been meaning to show more methods on how to prove the Earth is round. I’ve had a few ideas on how to do that, but got an interesting incentive when Phil Plait, The Bad Astronomer, wrote about the the Flat Earth Society . He claims it’s ridiculous to even bother rebutting the Flat Earth Society—and I tend to agree. But the history of our species’ intellectual pursuit is important and interesting. You don’t need to denounce all science and knowledge and believe in a conspiracy theory to enjoy some historical factoids about humanity’s quest for space .

On we go, to the top 10 ways to unequivocally, absolutely, positively prove the Earth isn’t flat.

1. Check the shadows on the moon

Now that humanity knows quite positively that the moon is not a piece of cheese or a playful god, the phenomena that accompany it (from its monthly cycles to lunar eclipses ) are well-explained. It was quite a mystery to the ancient Greeks, though, and in their quest for knowledge, they came up with a few insightful observations that helped humanity figure out the shape of our planet.

Aristotle (who made quite a lot of observations about the spherical nature of the Earth) noticed that during lunar eclipses (when the Earth’s orbit places it directly between the sun and the moon, creating a shadow in the process), the silhouette on the satellite’s surface is round. This shadow is the planet’s, and it’s a great piece of round-Earth evidence.

Since the earth is rotating (see the “ Foucault Pendulum ” experiment for a definite proof, if you are doubtful), the consistent oval-shadow it produces in each and every lunar eclipse proves that the earth is not only round but spherical—absolutely, utterly, beyond a shadow of a doubt not flat.

2. Follow ships on the horizon

If you’ve been next to a port lately, or just strolled down a beach and stared off vacantly into the horizon, you might have noticed a very interesting phenomenon: Approaching ships do not just “appear” out of the horizon like they should have if the world was flat, but rather seem to emerge from beneath the sea.

But, you say, ships do not submerge and rise up again as they approach our view (except in Pirates of the Caribbean , but we are hereby assuming that was a fictitious movie series). The reason ships appear as if they “emerge from the waves” is because the world is not flat: It’s round.

[Related: How old is Earth? It’s a surprisingly tough question to answer. ]

Imagine an ant walking along the surface of an orange, into your field of view. If you look at the orange “head on”, you will see the ant’s body slowly rising up from the “horizon” because of the curvature of the orange. If you would do that experiment with the ant approaching along a long road rather than a round object, the effect would change: The ant would slowly “materialize” into view (depending on how sharp your vision is).

3. Look up at the stars

This observation was originally made by Aristotle (384-322 BCE), who declared the Earth was round judging from the different constellations one sees while moving away from the equator.

After returning from a trip to Egypt, Aristotle noted , “There are stars seen in Egypt and … Cyprus which are not seen in the northerly regions.” This phenomenon can only be explained if humans were viewing the stars from a round surface, Aristotle continued, claiming that the sphere of the Earth is “of no great size, for otherwise the effect of so slight a change of place would not be quickly apparent.”

The farther you go from the equator, the farther the “known” constellations go towards the horizon, to be replaced by different stars. This would not have happened if the world was flat:

4. Conduct a stick test

If you stick a stick in the (sticky) ground, it will produce a shadow. The shadow moves as time passes (which is the principle for ancient Shadow Clocks ). If the world had been flat, then two sticks in different locations would produce the same shadow.

But they don’t. This, again, is because the Earth is round, and not flat.

Eratosthenes (276-194 BCE) used this principle to calculate the circumference of the Earth quite accurately. To see this demonstrated, refer to my experiment video about Eratosthenes and the circumference of the Earth.

5. Climb a hill or mountain

Standing on a flat plateau, you look ahead toward the horizon. You strain your eyes, then take out your favorite binoculars and stare through them, as far as your eyes (with the help of the binocular lenses) can see.

Next, climb up the closest tree—the higher the better, just be careful not to drop those binoculars and break their lenses. Then look again, strain your eyes, and stare through the binoculars out to the horizon.

[Related on PopSci+: How to not fear heights ]

The higher up you climb, the farther you will see. Usually, we tend to relate this to Earthly obstacles—like the fact we have houses or other trees obstructing our vision on the ground, and climbing upwards we have a clear view—but that’s not the true reason. Even if you stood on a completely clear plateau with no obstacles between you and the horizon, you would see much farther from the greater height than you would on the ground.

This phenomenon is caused by the curvature of the Earth as well, and would not happen if the Earth was flat:

6. Ride a plane

If you’ve ever taken a trip out of the country, specifically long-distance trips, you could notice two interesting facts about planes and the Earth:

• Planes can travel in a relatively straight line for a very long time and not fall off any edges. They can also circle the Earth without stopping .
• If you look out the window on a trans-Atlantic flight, you can, most of the times, see the curvature of the Earth on the horizon. The best view of the curvature used to be on the Concorde, but that plane’s long gone. I can’t wait to see the pictures from the new plane by Virgin Galactic—the horizon should look absolutely curved, as it actually is from a distance.

7. Scope out other planets

The Earth is different from other planets, that much is true. After all, we have life, and we haven’t found any other planets with life (yet). However, there are certain characteristics all planets have, and it will be quite logical to assume that if all planets behave a certain way, or show certain characteristics—specifically if those planets are in different places or were created under different circumstances—our planet is the same.

In other words: If so many planets that were created in different locations and under different circumstances show the same property, it’s likely that our own planet has the same property as well. All of our observations show that other planets are spherical (and since we know how they’re created, it’s also obvious why they take this shape). Unless we have a very good reason to think otherwise (which we don’t), our planet is very likely the same.

In 1610, Galileo Galilei observed the moons of Jupiter rotating around it . He described them as small planets orbiting a larger planet—a description (and observation) that was very difficult for the church to accept, as it challenged a geocentric model where everything was supposed to revolve around the Earth. This observation also showed that the planets (Jupiter, Neptune, and later Venus was observed too) are all spherical, and all orbit the sun.

[Related: Why is space cold if the sun is hot? ]

A flat planet (ours or any other planet) would be such an incredible observation that it would pretty much go against everything we know about how planets form and behave. It would not only change everything we know about planet formation, but also about star formation (our sun would have to behave quite differently to accommodate the flat-earth theory) and what we know of speeds and movements in space (like planets’ orbits and the effects of gravity). In short, we don’t just suspect that our planet is spherical. We know it.

8. Consider the existence of time zones

The time in New York, at the moment these words are written, is 12:00 p.m. The sun is in the middle of the sky (though it’s hard to see with the current cloud coverage). In Beijing, it’s 12:00 a.m., midnight, and the sun is nowhere to be found. In Adelaide, Australia, it is 1:30 a.m. More than 13 hours ahead. There, the sunset is long gone—so much so, that the sun will soon rise up again at the beginning of a new day.

This can only be explained if the world is round, and rotating around its own axis. At a certain point when the sun is shining on one part of the Earth, the opposite side is dark, and vice versa. That allows for time differences and time zones, specifically ones that are larger than 12 hours.

Another point concerning time zones, the sun, and Earth: If the sun was a “spotlight” (very directionally located so that light only shines on a specific location) and the world was flat, we would see the sun even if it didn’t shine on top of us (as you can see in the drawing below). Similarly, you can see the light coming out of a spotlight on a stage in the theater, even though you—the crowd—are sitting in the dark. The only way to create two distinctly separate time zones, where there is complete darkness in one while there’s light in the other, is if the world is spherical.

9. Feel the pull of gravity

Here’s an interesting fact about mass: It attracts things to it. The force of attraction (gravity) between two objects depends on their mass and the distance between them. Simply said, gravity will pull toward the center of mass of the objects. To find the center of mass, you have to examine the object.

Consider a sphere. Since a sphere has a consistent shape, no matter where on it you stand, you have exactly the same amount of sphere under you. (Imagine an ant walking around on a crystal ball. From the insect’s point of view, the only indication of movement would be the fact the ant is moving its feet—the shape of the surface would not change at all.) A sphere’s center of mass is in the center of the sphere, which means gravity will pull anything on the surface of the sphere straight down toward the center of the sphere. This will occur no matter where on the surface the object is located.

Consider a flat plane. The center of mass of a flat plane is in its center, so the force of gravity will pull anything on the surface toward the middle of the plane. That means that if you stand on the edge of the plane, gravity will be pulling you sideways toward the plane’s middle, not straight down like you usually experience when you stand on Earth.

I am quite positive that, even for Australians, an apple falls downwards, not sideways. But if you have your doubts, I urge you to try dropping something—just make sure it’s nothing that can break or hurt you.

[Related: Have we been measuring gravity wrong this whole time? ]

Here is some further reading about the center of mass and distribution of mass . And if you are brave enough to handle some equations (not involving integration), you can learn more about Newton’s Law of Universal Gravitation .

10. Browse images from space

In the past 60 years of space exploration, we’ve launched satellites, probes, and people into space. Some of them got back, some of them still float through the solar system (and almost beyond it), and many transmit amazing images to our receivers on Earth. In all of these photos, the Earth is (wait for it) spherical. The curvature of the Earth is also visible in the many photos snapped by astronauts aboard the International Space Station . You can see recent examples on the ISS Instagram account .

You know what they say—a picture is worth a thousand diss tracks .

This post has been updated. It was originally published in January 2016.

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Round Earth Clues: How Science Proves that our Home is a Globe

Do you want to prove that the Earth is round?

Hop on a plane, and fly to Cape Town, South Africa, or Melbourne, Australia — two major cities located in the Southern Hemisphere. There, you won’t be able to see the North Star.

This might seem like an expensive trip, but it’s one part of an experiment that can be done to disprove the Flat Earth theory — a theory at the center of a popular new documentary — Behind the Curve — that is now streaming on Netflix.

The documentary follows several people who espouse the Flat Earth Theory, which is the belief that the Earth is a plane or a disk, and try to generate support for their cause through Internet videos, social media, podcasts, meetings, and even international conferences.

Jason Steffen , an assistant professor of physics and astronomy at UNLV, works in the field of exoplanets (planets that orbit distant stars) and has a history in experimental studies of dark matter, dark energy, and gravity. For more than 10 years, Steffen was also a member of the science team for NASA’s Kepler mission. Discoveries from that mission revolutionized our understanding of planets and planetary systems, Steffen said.

As such, he was able to help us break down reasons why the Flat Earth Theory falls flat. 

OK, so how do we know — scientifically — that the Earth is a sphere?

At a very basic level, we can see the Earth’s curvature through satellites that we’ve launched into space. Additionally, through the use of high-powered telescopes, we’ve been able to examine planets both in our solar system and beyond, and all of them are spherical in shape.

There is a very deep, fundamental reason why the Earth is round: the force of gravity depends upon the distance between two interacting objects, and the only three-dimensional object you can make with a single distance is a sphere.  We can measure the behavior of gravity in the laboratory with a variety of highly sensitive experiments.  Each of these experiments shows that the force of gravity depends only on the mass of the two objects and the distance between them.  If, on the other hand, you wanted to form a flattened object using gravity alone, the force of gravity would have to depend upon two, perpendicular distances in two perpendicular directions.

Now, let’s backtrack to the time before satellites and telescopes. Why did people once think that the Earth was flat?

The primary reason that ancient people believed that the Earth was flat was that it looks flat from our vantage point on the ground. Most people throughout history never traveled more than a few miles from their place of birth, so the horizon that they saw was always the same.  Moreover, most people were more worried about meeting the necessities of life than they were about the shape of the Earth.

The misconception that the Earth must be flat because it looks flat to us arises simply because the Earth is big. The height of an adult is much less than one millionth of the Earth's radius. In order to see the curvature of the Earth in a single field of view, you would need to be perched above the surface a sizable fraction of that radius, and one millionth wouldn't be considered "sizable.”

What clues changed their thinking?

This state of affairs started to change about 2,500 years ago during the Iron Age, especially with the Greeks. There are two primary reasons that the Greeks knew the Earth was round:

• Lunar eclipses. First, they saw that during a lunar eclipse the shadow of the Earth always had a round profile. This happened regardless of the time of night that the eclipse occurred, the season, or the direction that the shadow crept across the Moon's surface. The only object that casts a circular shadow no matter how you shine a light across it is a sphere. Any other shape would not be able to cast a round shadow under this variety of circumstances.
• Star patterns. The second observation is how the pattern of stars changes as you move north and south. If you were to stand at the North Pole, Polaris (the North Star), would be directly overhead. On a flat Earth, Polaris would always be visible — no matter how far away from the North Pole you moved, it would still be above the horizon. However, by the time you reach the equator, Polaris is on the northern horizon, and it disappears entirely once you move into the southern hemisphere. You can't see Polaris from Australia. In fact, the ancient Greeks calculated the circumference of the Earth using this effect and produced an answer that was strikingly close to what we measure today.

If you want to prove that the Earth is a sphere, here’s an experiment you can do today: Quito, Ecuador and Nairobi, Kenya are two cities on the equator. Fly to either and you'll see Polaris on the northern horizon. Cape Town, South Africa and Melbourne, Australia are well south of the equator. Fly to either and you won't see Polaris at all. A few minutes drawing the predictions of the two competing models on a piece of paper is sufficient to exclude one of those models. And, this isn't the only demonstration you can do from the ground.

Flat Earth theorists say that if the Earth is a spinning sphere, why can’t they feel it? How did scientists first prove that the Earth rotates?

Though the shape of the Earth had been settled for over two millennia, a scientist by the name of Leon Foucault designed an experiment in 1851, using a very long pendulum, that showed both that the Earth is round and that it rotates. If you place the pendulum at the North Pole, the direction of its swing changes with respect to the ground and completes a full circle each day. Placing the same pendulum on the equator yields no change at all in the direction of the swing. These facts, and the behavior of the pendulum when it is placed anywhere else, agree with Foucault's prediction.

Are there other clues that prove the Earth spins on its axis?

We can see the effects of the Earth's shape and rotation in several other ways:

• The six jet streams on the Earth — and how their directions relate to each other — is a consequence of the Earth's shape and rotation.
• Artillery gunners must correct for the rotation of the Earth as the shell flies through the air above the surface.
• Modern naval guns can shoot far over their visible horizon due to the Earth's curvature.
• Hurricanes and (most) tornadoes rotate counter-clockwise in the northern hemisphere while they rotate clockwise in the southern hemisphere. Fun fact: Toilets and sinks are too small to reliably reproduce this effect, despite the rumors that they flush or drain in the opposite direction in the southern hemisphere.

The next time you’re at a party, impress your friends with this enlightening experiment

Hold a pencil in front of you, looking down at the tip. Rotate it so that its tip is spinning counter-clockwise. Keep rotating it with your fingers in the same direction as you slowly turn the pencil over so that you are looking at its eraser. Now, the eraser will be spinning clockwise. Slowly rotate it back, while continuing its spin, will bring the tip to the top, rotating counter-clockwise.

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Flat vs. Round Earth Calculator

Belief in a flat earth, the flat earth model, sunset twice experiment, directions to see a sunset twice, disappearing object experiment, instructions for hiding an object behind the curvature of the earth, stick shadow experiment, instructions for measuring how big the earth is using stick shadows, example calculation of a stick shadow experiment, what happens in the stick shadow experiment if the earth is flat.

What is the best way to learn about the world? Propose a theory and set out to prove it with observations (science)? Or just make stuff up and ignore obvious facts (nonsense)? Here at Omni, we tend to think the first option is doing pretty well. It got us to the Moon, didn't it? – It really did, by the way.

To celebrate World Science Day for Peace and Development , held every 10 November, we've created a calculator that helps you fight against bunkum, half-truths and baloney, and for science, observation, and open-mindedness .

Omni's flat vs. round Earth calculator features experiments that help prove that the Earth is indeed round. Don't worry; you won't be building your own rocket to go into outer space to check (or calculate its impulse and momentum or its kinetic energy ).

We have three relatively simple experiments for you to try:

Sunset twice — By changing your viewpoint above the ground, you can see a sunset twice. Our calculator tells you how much of the second sunset you will see.

Disappearing objects — Hide objects behind the curvature of the Earth by changing the height of your viewpoint. This calculator will show you how tall an object you can make disappear.

Stick shadows — Use the lengths of shadows cast by a stick at different locations to estimate the circumference of the Earth.

Before we get to the experiments, let's briefly overview why people might believe in a flat Earth and the model of the world they put forward.

Amazingly, in the richest, most technologically developed country in the world, one in six of the population are not sure if the Earth is round 🤔. Of course, the country is the USA , and belief in a flat Earth may stem from its highly individualistic culture and a distrust of authority, institutions, and experts.

Flat Earthers seem to look at the world all on their own, without reference to the well over 2,000 years of human discovery . Wow, they are missing out. They are also extremely distrustful of any facts that they haven't verified for themselves personally. Talk about trust issues.

They then take on extraordinary challenges to prove the Earth is flat when there are simple things they could do to prove the Earth is round. Here are some examples:

• "Mad" Mike Hughes built his own steam-powered rockets to fly to a height of 1,800 feet (550 m) to photograph the lack of curvature of the Mojave Desert. Unfortunately, you need to go up to at least 35,000 feet (11,000 m) to see the curvature of the Earth. He sadly passed away in February 2020 in a failed rocket flight.
• YouTube star Logan Paul was planning to visit Antarctica to find the edge of a flat Earth. However, the trip did not occur due to the COVID-19 pandemic and the lack of medical facilities to support any emergencies.
• Rapper B.o.B tried to crowdfund his own satellite launch to check for a flat Earth. He only managed to raise $6,883 of his $1 million goal. Oh well, never mind. Maybe he could try out our simple, low-cost experiments instead.

This cartoon by Tom Fonder sums up flat Earthers quite nicely.

In the flat Earth model, the world is a disk (similar to the gears used for gear reduction ) with the north pole at the center. Around the edge of the disk is the ice and snow of the "south pole." This then forms an icy barrier, presumably to stop the water of the oceans from falling off of the disc into space.

The thickness of the flat Earth disk is not clear. However, the mass involved must be much less than a round Earth, so Earth wouldn't be able to hold on to its atmosphere. Maybe there is a transparent dome over the Earth, stopping it from escaping.

The traditional flat Earth model has the sun positioned over the disk, circling around in the sky like a baby's mobile and at a much closer distance. That then doesn't explain sunsets and sunrises. For some sanity, let's imagine the disk spins like a coin relative to the sun. That would at least get our sunrise and sunset back (something the simplest animal could observe). However, there would be no timezones as sunrise and sunset would be at the same time all over the world.

🔎 💻 You can experience what it's like to live on a flat Earth using a computer model created by Bruce Sherwood. It shows the sun never setting and its apparent size changing throughout the day, plus many other things we simply don't observe in reality.

That's the main problem with the flat Earth model. It's full of inconsistencies and unexplained observations. For example, why is it cold at both the center and the edge of the disk?

Let's get back to a more scientific way of thinking and introduce the first experiment.

This first experiment can be really simple to perform. Move upwards quick enough to get ahead of the shadow cast by the horizon. You’ll then be able to see part of the sunset twice! If you observe this, then the Earth is indeed round. This experiment will calculate how much of a second sunset you could see and how long you could make a sunset last.

What would you see if the Earth was flat? No second sunset 😭. No matter how high or fast you traveled up from the surface of a flat Earth; you wouldn't see the sun again until dawn.

For a round Earth, as the sun sets, imagine the shadow cast by the Earth's horizon coming towards you and moving up your body. If you can get ahead of this shadow by moving upwards fast enough, you can see the sunset again. Let's take a look at the math.

This paper gives us an equation that relates time with the height of the shadow:

t = 8 × √h ,

where t is the time it takes the shadow to move up in height by the amount h . We can relate h to the height difference between two heights and t to the time it takes to move upwards. Because we can't instantly travel from the lower to the higher height, we need to consider the travel time. Finally, to find the amount of a second sunset we can see again, we need to know the sunset duration. We then have this equation for the percentage of the sunset two you will observe again:

Sunset two percentage = 100 × (1 - ((Sunset duration - t - Travel time) / Sunset duration))

There are a few ways to see the sun again just after it has set, to varying degrees. Omni's flat vs. round Earth calculator will tell you how much of a second sunset you will be able to observe. Let's go through three ideas we've come up with.

1. Lie down, stand up

This idea is the simplest in terms of equipment. You just need a location where you can see the sun setting into the sea or very flat land (like a desert). A beautiful cloudless sky will also help. All you need to do is watch the sunset while lying down. Once you can't see any of the Sun anymore, immediately stand up as fast as you can. You should be able to see a small part of the top of the sun again.

Here's how to use the calculator to compute precisely how much.

• Select a location closest to you or manually enter the sunset duration where you are.
• Enter the lower starting height of your eye-level. In this case, when lying down. We recommend about 8 inches (20 cm).
• Input how long it will take you to get to the higher height. We reckon about half a second but do go ahead and time yourself to double-check.
• Enter the final height of your eye-level when you are standing up. You can measure this by subtracting the distance from the top of your head to your eyes away from your height.
• You will then see the percentage of the sun you'll be able to see set again. Want to see more? Try changing the values in the calculator or go to the more advanced variations of the experiment below.

You should be able to see around 5% of the second sunset with this method.

2. Fast lift up a skyscraper

To see more of the second sunset, you're going to have to go higher and faster to get ahead of the horizon's shadow. A skyscraper with a fast lift is one option. This phenomenon has been observed at the Burj Khalifa hotel in Dubai.

To select the input values for this skyscraper, choose "Sky scrapper lift – Burj Khalifa hotel" from the ideas list. If you want to try this at another building, adjust the input values accordingly.

You should be able to see a massive 88% of the sunset again, and so nearly doubling the duration. If you are a sunset lover, this is the thing to do.

3. Drone with a camera

Another idea is to use a good-quality drone that has a live streaming camera capability. We found one drone that can reach 3,300 feet (1,000 m) in 200 seconds. If you select "Drone" from the list of ideas, you'll see that you should see about a third of the sunset again with this method.

Check how fast and high your drone can go and adjust the values in the calculator accordingly.

In this experiment, we will hide part of an object behind the curvature of the Earth. You will need to find a body of water where the far shore is at least a mile and a quarter away (2 km), and it needs to be a nice calm day with no wind.

Also, to help avoid the mirage effect (light refraction), do the experiment in the morning when it's cool. That's also why we don't recommend using a desert – the mirage effect will mean you won't be able to see objects on the far shore clearly enough.

In this YouTube video, the guy made a truck 4 miles (7 km) away disappear on the far side of a lake by lowering his camera closer to the ground.

Alternatively, an off-shore wind farm is also a good option, as this photograph demonstrates:

Notice the further away a windmill is, the more of it is hidden. That's what this experiment is about – calculating how much of a distant object you can hide behind the curvature of the Earth.

💡 The curvature of the Earth has been measured as 8 inches per mile (12 cm per kilometer). That means that for every mile you are away from an object, 8 inches of the bottom of the object is hidden by the curvature of the Earth. However, that does assume you are looking at the object a zero height, which is not very practical.

In this experiment, we will start at a high viewpoint and then go down to a low viewpoint to obscure a distant object . In math terms, we find how much is hidden at the high and low views and calculate the difference.

To calculate the obscured height, we first need to know the distance to the horizon. This is given by this equation:

a = √[(r + h)² - r²]

• a is the distance to the horizon,
• h is viewpoint level above the ground, and
• r is the Earth's radius, equal to 3,959 miles or 6,371 km.

Then we input the result into a second equation that calculates how much of the object is obscured, x , if viewed from zero height:

x = √(a² - 2ad + d² + r²) - r

The difference in the two values of x is the height of the object we can make disappear by changing our viewpoint.

OK, so you've found an excellent location, such as a lake with shores a few miles apart. To see any objects on the far shore, you will need some good binoculars . Better still, a video camera with a powerful zoom lens. That would also allow you to record the experiment, just like in the video above.

To get a steady view through your binoculars or camera, mounting them on a tripod is recommended. Using a tripod also allows you to measure the two heights accurately.

Here is how to use the calculator to figure out what size object you might be able to disappear behind the curvature of the Earth.

• Measure the distance to the far shore of the lake. You can use a paper map or the measuring feature on Google Maps to do this. Input the distance into the "Distance to object" variable in the calculator.
• Measure the height above the ground of your eye-level while standing up or your camera when it is in the high height position. Enter this height in the next input field.
• Do the same when you are lying down, or your camera is in the low height position. To maximize the effect, try to get as low to the water level as possible.
• You'll then see the height of an object that is obscured by the Earth’s curvature is calculated for you. If it seems too small to see, try increasing your high height and decreasing your low height.

If the Earth is flat, you wouldn't see any difference in the objects on the far side of the lake, no matter how low to the ground you view them.

This experiment not only proves the Earth is round, you can also estimate the circumference of the Earth. This is precisely what Greek mathematician Eratosthenes did in Alexandria, in around 240 BC . He knew that in Aswan, around 500 miles to the south, there was a well where sunlight reached the bottom at noon on the summer solstice. At the same time, he measured the shadow cast by a stick in Alexandria.

Assuming the Earth is round and the sun is far away, and using the mathematics we'll go through below, he concluded that the Earth's circumference was about 50 times the distance between Alexandria and Aswan. That is within 10% of the correct answer . A fantastic result for such a simple experiment performed over 2,000 years ago.

💡 Earth's circumference is the distance around the Earth. Measuring around the poles it's 24,860 miles (40,008 km). Measuring around the equator it's 24,901 miles (40,075 km). The slight difference between the two measurement is because the Earth spins.

Looking at the triangle formed by the stick and the shadow, we can use the inverse tangent trigonometry function to calculate the angle between the stick and the sunlight ray, using the equation:

θ = arctan(Shadow length / Stick height)

So we do that for the two locations. How do these two angles relate to the circumference of the Earth? The figure below will help us to answer this question.

Using some geometry, we can show that the angle α between lines that go through locations A and B, and the center of the Earth, is the difference in the stick shadow angles:

α = θ₂ - θ₁

We now know the arc length (distance along the surface of the Earth) between A and B, and the angle α. This allows us to simply scale up the distance to the full Earth circumference, using the equation:

Earth circumference = Distance A → B × (360° / α)

It's important to note that the distance from A to B should be the distance if you could only travel north or south (the north-south distance). We need this distance as it is only when you travel northwards does the shadow cast by the stick gets longer.

Assuming point A is south of point B, on a map, draw a line due north from point A. Then draw a line due east from point B. The north-south distance is the length from point A to where the two lines you drew cross over each other.

There are two main ways you can try this experiment. You can either travel a considerable distance north or south (greater than 100 miles, but the further, the better) or partner up with someone who lives far away to help you.

Let's start with the traveling option. It's best to attempt this around the shortest or longest day of the year, as the day length is relatively stable. That will reduce errors in the shadow angle measured at the two locations. Here are step-by-step instructions:

• Measure the length of your stick . You'll need to enter this into the first input field of the calculator. If part of the stick is in the ground, only include the length above the ground.
• Measure the length of the shadow at location A at local noon time. If it's not a sunny day, wait until you get one. Input the shadow length into the calculator, and the shadow angle will be calculated for you.
• Travel to location B and do the same as in step 2.
• Using a map, measure the north-south distance between the two locations and enter this figure into the calculator (see instructions above).
• You'll then receive an answer to your measured estimate of the Earth's circumference and how close you got to the real answer.

If you have a friend at another location to help you, that's even better! The experiment will be the most accurate if you do both measurements on the same day of the year and at the same solar time. In this case, the steps are basically the same. Make sure the two sticks are the same length and that you measure the shadow at noon local time on the same day. This option is a lot easier and can be performed on any sunny day of the year.

For an example, let's travel north from Florida to Pennsylvania (A to B), covering a north-south distance of around 1,000 miles (1,609 km). The stick is 3 feet (0.91 m) long, and we measure a shadow length of 3 feet at A. That means a shadow angle of 45°. We then travel to B and measure a shadow of 5.2 feet, which means the shadow angle here is about 60°.

Enter all these figures into the calculator, and we get a result of 23,971 miles (38,577 km) . That's within 4% of the real circumference as measured between the poles of 24,860 miles (40,008 km).

Let's imagine that the flat-earthers are right for a moment. How does the above example work in a flat Earth model?

In a flat earth model, sticks will still cast a shadow of different lengths. However, the result of doing some trigonometry leads to a strange result. Referring to the above diagram and applying said trigonometry, we can say that:

d = h × |tan θ₂ - tan θ₁|

Using the angles 45° and 60°, and 1,000 miles for d, we see that the distance to the sun h is

h = 1,000 / (1.73 - 1) = 1,370 miles

That does seem very close. However, the flat earth model can say the sun is much smaller than science has concluded.

Now we can calculate the two other distances to the sun from the two locations:

R₁ = h / cos θ₁ = 1370 / cos(45°) = 1937 miles

R₂ = h / cos θ₂ = 1370 / cos(60°) = 2740 miles

This result means that by traveling south 1,000 miles, the sun should have got smaller by around 40% . In reality, as you can verify for yourself, the sun does not appear to get smaller as you travel southwards.

Therefore, we can conclude that the flat Earth model is wrong. It does not agree with observation. That is the crucial property of any scientific model. It must agree with experimental results.

When did we learn that the Earth is round?

The notion that the Earth is spherical is quite old! In Ancient Greece, scientists and philosophers were aware of this fact as early as the V century B.C.

Even in later centuries, the spherical model was more widely accepted and only marginally questioned outside purely mythological grounds: this theory's apparent resurgence and relevance in modern times is purely a consequence of the change in our communication methods .

How do I calculate the circumference of the Earth using shadows?

To calculate the circumference of the Earth using shadows:

• Ask a friend living at a different latitude to perform the same steps as you; then:
• Vertically plant a stick of known length in the ground.
• Measure the angle between the stick and the sun rays at a given time of the local day.
• Use the formula: θ = arctan(Shadow length / Stick height) .
• Distance is the north-south distance between the sticks; and
• α is the difference between the angles calculated before.

How high should I be to see the curvature of Earth?

To see the curvature of the Earth, you must be at an altitude of around 35,000 ft or 10.5 km . This is about the cruising altitude of a passenger plane. However, to see it properly, you need a completely clear horizon (no clouds) and a field of view of at least 60 degrees . Both these conditions are rarely satisfied from the windows of your plane, but you can try.

Also, notice that the curvature is not visible even from the summit of Mt. Everest!

How can I prove that the Earth is round?

To prove that the Earth is round, go to the beach! If there is a long enough stretch of sea in front of you, you can simply wait for a ship to approach the coast. You will first see its top part appearing above the horizon, slowly followed by the rest of the ship. As the Earth is round, its curvature covers part of the ship. The covered part gets smaller as the ship approaches you.

Now, the hard part is to convince skeptics that this is a definitive answer!

• Select your location or input the sunset duration where you are.
• Choose an idea to gain height or input custom starting height, time and final height.
• If the calculator says you can see part of a second sunset again and you did, you just proved the Earth is round!

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Mileage Calculator

Use the following mileage calculator to determine the travel distance, in terms of miles, and time taken by car to travel between two locations in the United States, disregarding traffic conditions.

How long does it take to get to Mars?

We explore how long it takes to get to Mars and the factors that affect a journey to the Red Planet.

• Distance to Mars
• Traveling at the speed of light

Fastest spacecraft so far

Mars travel time q&a with an expert.

• Travel time calculation problems
• Past mission's travel times

Additional resources

Ever wondered how long does it take to get to Mars? 

The answer depends on several factors, ranging from the position of Earth and Mars to the technology that would propel you there. According to NASA , a one-way trip to the Red Planet would take about nine months . If you wanted to make it a round-trip , all in all, it would take about 21 months as you will need to wait about three months on Mars to make sure Earth and Mars are in a suitable location to make the trip back home. 

We take a look at how long a trip to the Red Planet would take using available technology and explore some of the factors that would affect your travel time.

Related: Curiosity rover: 15 awe-inspiring photos of Mars (gallery) 

How far away is Mars?

To determine how long it will take to reach Mars, we must first know the distance between the two planets.

Mars is the fourth planet from the sun, and the second closest to Earth (Venus is the closest). But the distance between Earth and Mars is constantly changing as they travel around the sun .

In theory, the closest that Earth and Mars would approach each other would be when Mars is at its closest point to the sun (perihelion) and Earth is at its farthest (aphelion). This would put the planets only 33.9 million miles (54.6 million kilometers) apart. However, this has never happened in recorded history. The closest recorded approach of the two planets occurred in 2003 when they were only 34.8 million miles (56 million km) apart.

The two planets are farthest apart when they are both at their farthest from the sun, on opposite sides of the star. At this point, they can be 250 million miles (401 million km) apart.

The average distance between Earth and Mars is 140 million miles (225 million km).

Related: What is the temperature on Mars?

How long would it take to travel to Mars at the speed of light?

Light travels at approximately 186,282 miles per second (299,792 km per second). Therefore, a light shining from the surface of Mars would take the following amount of time to reach Earth (or vice versa):

• Closest possible approach: 182 seconds, or 3.03 minutes
• Closest recorded approach: 187 seconds, or 3.11 minutes
• Farthest approach: 1,342 seconds, or 22.4 minutes
• On average: 751 seconds, or just over 12.5 minutes

The fastest spacecraft is NASA's Parker Solar Probe , as it keeps breaking its own speed records as it moves closer to the sun. On Nov 21, 2021, the Parker Solar Probe reached a top speed of 101 miles (163 kilometers) per second during its 10th close flyby of our star, which translates to a phenomenal 364,621 mph (586,000 kph). According to a NASA statement , when the Parker Solar Probe comes within 4 million miles (6.2 million kilometers) of the solar surface in December 2024, the spacecraft's speed will top 430,000 miles per hour (692,000 kph)!

So if you were theoretically able to hitch a ride on the Parker Solar Probe and take it on a detour from its sun-focused mission to travel in a straight line from Earth to Mars, traveling at the speeds the probe reaches during its 10th flyby (101 miles per second), the time it would take you to get to Mars would be:

• Closest possible approach: 93 hours 
• Closest recorded approach: 95 hours  
• Farthest approach: 686 hours (28.5 days)  
• On average: 384 hours (16 days)  

We asked Michael Khan, ESA Senior Mission Analyst some frequently asked questions about travel times to Mars. 

Michael Khan is a Senior Mission Analyst for the European Space Agency (ESA). His work involves studying the orbital mechanics for journeys to planetary bodies including Mars.

How long does it take to get to Mars & what affects the travel time?

The time it takes to get from one celestial body to another depends largely on the energy that one is willing to expend. Here  "energy" refers to the effort put in by the launch vehicle and the sum of the maneuvers of the rocket motors aboard the spacecraft, and the amount of propellant that is used. In space travel, everything boils down to energy. Spaceflight is the clever management of energy.

Some common solutions for transfers to the moon are 1) the Hohmann-like transfer and 2) the Free Return Transfer. The Hohmann Transfer is often referred to as the one that requires the lowest energy, but that is true only if you want the transfer to last only a few days and, in addition, if some constraints on the launch apply. Things get very complicated from there on, so I won't go into details.

Concerning transfers to Mars, these are by necessity interplanetary transfers, i.e., orbits that have the sun as central body. Otherwise, much of what was said above applies: the issue remains the expense of energy. An additional complication lies in the fact that the Mars orbit is quite eccentric and also its orbit plane is inclined with respect to that of the Earth. And of course, Mars requires longer to orbit the sun than the Earth does. All of this is taken into account in a common type of diagram called the "pork chop plot", which essentially tells you the required dates of departure and arrival and the amount of energy required.

The "pork chop plot" shows the trajectory expert that opportunities for Mars transfers arise around every 25-26 months, and that these transfers are subdivided into different classes, one that is a bit faster, with typically around 5-8 months and the other that takes about 7-11 months. There are also transfers that take a lot longer, but I’m not talking about those here. Mostly, but not always, the second, slower one turns out to be more efficient energy-wise. A rule of thumb is that the transfer to Mars takes around as long as the human period of gestation, approximately 9 months. But that really is no more than an approximate value; you still have to do all the math to find out what applies to a specific date.

Why are journey times a lot slower for spacecraft intending to orbit or land on the target body e.g. Mars compared to those that are just going to fly by?

If you want your spacecraft to enter Mars orbit or to land on the surface, you add a lot of constraints to the design problem. For an orbiter, you have to consider the significant amount of propellant required for orbit insertion, while for a lander, you have to design and build a heat shield that can withstand the loads of atmospheric entry. Usually, this will mean that the arrival velocity of Mars cannot exceed a certain boundary. Adding this constraint to the trajectory optimisation problem will limit the range of solutions you obtain to transfers that are Hohmann-like. This usually leads to an increase in transfer duration.

The problems with calculating travel times to Mars

The problem with the previous calculations is that they measure the distance between the two planets as a straight line. Traveling through the farthest passing of Earth and Mars would involve a trip directly through the sun, while spacecraft must of necessity move in orbit around the solar system's star.

Although this isn't a problem for the closest approach, when the planets are on the same side of the sun, another problem exists. The numbers also assume that the two planets remain at a constant distance; that is, when a probe is launched from Earth while the two planets are at the closest approach, Mars would remain the same distance away over the length of time it took the probe to travel. 

Related: A brief history of Mars missions

In reality, however, the planets are moving at different rates during their orbits around the sun. Engineers must calculate the ideal orbits for sending a spacecraft from Earth to Mars. Like throwing a dart at a moving target from a moving vehicle, they must calculate where the planet will be when the spacecraft arrives, not where it is when it leaves Earth. 

It's also not possible to travel as fast as you can possibly go if your aim is to eventually orbit your target planet. Spacecraft need to arrive slow enough to be able to perform orbit insertion maneuvers and not just zip straight past their intended destination. 

The travel time to Mars also depends on the technological developments of propulsion systems.

According to NASA Goddard Space Flight Center's website, the ideal lineup for a launch to Mars would get you to the planet in roughly nine months. The website quotes physics professor Craig C. Patten , of the University of California, San Diego:

"It takes the Earth one year to orbit the sun and it takes Mars about 1.9 years (say 2 years for easy calculation) to orbit the sun. The elliptical orbit which carries you from Earth to Mars is longer than Earth's orbit but shorter than Mars' orbit. Accordingly, we can estimate the time it would take to complete this orbit by averaging the lengths of Earth's orbit and Mars' orbit. Therefore, it would take about one and a half years to complete the elliptical orbit.

"In the nine months it takes to get to Mars, Mars moves a considerable distance around in its orbit, about three-eighths of the way around the sun. You have to plan to make sure that by the time you reach the distance of Mar's orbit, Mars is where you need it to be! Practically, this means that you can only begin your trip when Earth and Mars are properly lined up. This only happens every 26 months. That is, there is only one launch window every 26 months."

The trip could be shortened by burning more fuel — a process not ideal with today's technology, Patten said.

Evolving technology can help to shorten the flight. NASA's Space Launch System (SLS) will be the new workhorse for carrying upcoming missions, and potentially humans, to the red planet. SLS is currently being constructed and tested, with NASA now targeting a launch in March or April 2022 for its Artemis 1 flight, the first flight of its SLS rocket.

Robotic spacecraft could one day make the trip in only three days. Photon propulsion would rely on a powerful laser to accelerate spacecraft to velocities approaching the speed of light. Philip Lubin, a physics professor at the University of California, Santa Barbara, and his team are working on Directed Energy Propulsion for Interstellar Exploration (DEEP-IN). The method could propel a 220-lb. (100 kilograms) robotic spacecraft to Mars in only three days, he said.

"There are recent advances which take this from science fiction to science reality," Lubin said at the 2015 NASA Innovative Advanced Concepts (NIAC) fall symposium . "There's no known reason why we cannot do this." 

How long did past missions take to reach Mars?

Here is an infographic detailing how long it took several historical missions to reach the Red Planet (either orbiting or landing on the surface). Their launch dates are included for perspective. 

Explore NASA's lunar exploration plans with their Moon to Mars overview . You can read about how to get people from Earth to Mars and safely back again with this informative article on The Conversation . Curious about the human health risks of a mission to the Red Planet? You may find this research paper of particular interest.  

Bibliography

• Lubin, Philip. " A roadmap to interstellar flight. " arXiv preprint arXiv:1604.01356 (2016). 
• Donahue, Ben B. " Future Missions for the NASA Space Launch System. " AIAA Propulsion and Energy 2021 Forum . 2021. 
• Srinivas, Susheela. " Hop, Skip and Jump—The Moon to Mars Mission. " (2019). 

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

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Nola Taylor Tillman is a contributing writer for Space.com. She loves all things space and astronomy-related, and enjoys the opportunity to learn more. She has a Bachelor’s degree in English and Astrophysics from Agnes Scott college and served as an intern at Sky & Telescope magazine. In her free time, she homeschools her four children. Follow her on Twitter at @NolaTRedd

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