Why globe is round

But some of them are still minor objects in the Solar system. These bits of leftover planet-building material, called asteroids and comets, have very lumpy shapes. Some are shaped like potatoes and others like eggs. The largest of these minor bodies, such as Ceres and Pluto, have enough gravity to look round like a planet. They are called dwarf planets. Some, like Haumea, spin very fast, giving them an stretched shape, like this:. Hello, curious kids! Ask an adult to send your question to us.

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The mass of the Earth is big enough that the gravitational force it creates can pull the hard shape of ice, rock and metal into a sphere. Moreover, to even out Earth's imbalanced distribution of mass and stabilize its spin, "the entire surface of the Earth will rotate and try to redistribute mass along the equator, a process called true polar wander," Meert says.

To keep track of Earth's shape, scientists now position thousands of Global Positioning System receivers on the ground that can detect changes in their elevation of a few millimeters, Gross says.

Another method, dubbed satellite laser ranging, fires visible-wavelength lasers from a few dozen ground stations at satellites.

Any changes detected in their orbits correspond to gravitational anomalies and thus mass distributions inside the planet. Still another technique, very long baseline interferometry, has radio telescopes on the ground listen to extragalactic radio waves to detect changes in the positions of the ground stations.

It may not take much technology to understand that Earth is not perfectly round, but it takes quite a bit of effort and equipment to determine its true shape. Charles Q. Choi is a frequent contributor to Scientific American. In his spare time, he has traveled to all seven continents. Follow Charles Q. Choi on Twitter. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue.

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?

Why did people once think that the Earth was flat? 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.

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. How did scientists first prove that the Earth rotates? 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. March 11 Author: Jason Steffen , Natalie Bruzda. Media Contact: Natalie Bruzda ; natalie. Topics: astronomy , College of Sciences , science and technology , tips topics trends.