Earth is a planet in our solar system. It is the only planet not named after a god and is the most dense planet in the solar system.
About 4.5 billion years ago, the Earth was a hot molten ball of rock and minerals. Rivers of lava rushed across its surface.
1. The Earth is a sphere
A sphere is a three-dimensional shape that is round and has no edges or vertices. It is the second cousin of a circle, and can be found in many objects. Examples include playing balls, balloons, and light bulbs.
A spherical Earth is one of the most common models for modeling a planet in geodesy, a science that helps scientists understand and measure the size and shape of a planet. It is a useful approximation for determining the location and orientation of land, water, and buildings on Earth.
Scientists have been using this model for centuries to help them build models of the solar system and the universe. They also use it to model astronomical phenomena and the behavior of celestial bodies.
The shape of a sphere is determined by the distance between its center and its surface (called the radius). It also has a diameter (called the circumference), a surface area, and volume.
There are many different spheres, including the oblate spheroid, which has a smooth surface and is the most stable of the three spherical shapes. An oblate spheroid has a circular orbit around the Sun, which is what makes it spherical.
Because the Earth is a spherical body, gravity pulls it towards its center. But the force of rotation also causes it to bulge slightly at the equator. This is what explains why the Earth appears to be slightly flat from the ground, even though it is round!
Astronomers and mathematicians have known about a spherical Earth since the ancient Greeks. Aristotle, for instance, wrote in 350 B.C. that we could see the stars and know that the Earth was round based on observations of the way we would see them depending on where we were in the sky.
Other evidence that the Earth is round includes the shadows that we cast on the Moon during lunar eclipses. These shadows change a lot depending on where we are in the sky, and they look very different if the Earth is flat.
Unlike flat Earth theorists, most people agree that our planet is round and not a flat disc or sphere. They also have an intuitive understanding of the shape of our planet. In fact, people in the ancient world knew that our planet was round and didn’t believe it was flat, like Christopher Columbus.
2. The Earth is shaped like an oblate spheroid
The Earth is not a perfect sphere; it is actually an oblate spheroid. This is a type of shape that is found in many planets and some stars. This shape is caused by the fact that the planet is spinning on its axis.
This rotation makes it swell more at the equator than at the poles. This swell gives the Earth its shape of an oblate spheroid.
Because the Earth is a spheroid, it has two axes: a major axis and a minor axis. The minor axis goes through the center of the ellipse and has its end points positioned at minimum distance from the major axis.
Another thing about an oblate spheroid is that it is slightly flattened at the poles. This is because the gravity on the Earth is stronger at the poles than at the equator. This is why the equator has a slightly greater radius than the poles.
It is this difference in gravity that causes the equator to bulge out, making the Earth seem like an oblate spheroid. The Earth’s oblate spheroid shape is important to science because it can help explain why the planet is different from other bodies in our solar system.
This shape is also useful in calculating the gravity field of an anomalous mass, such as a satellite or an ocean floor. These measurements are dominated by the overall gravity field of the planet, but this must be removed to get accurate measurements.
As a result, surveys in various regions of the world often produce different ellipsoidal parameters. For example, surveys in Australia produced different ellipsoidal parameters than those in South America or Asia.
Although the ellipsoidal deviations are not very big, they do affect large-scale maps. For example, the elliptical deviation of the South Pole is greater than the elliptical deviation of the North Pole.
This can be a problem for scientists because they are trying to figure out how to keep track of changes in the Earth’s shape. Luckily, they have a few techniques that can help them. One of them is called satellite laser ranging, which uses lasers from thousands of Global Positioning System receivers on the ground to measure changes in Earth’s elevation.
3. The Earth is rotating
Every day, the Earth completes a rotation on an invisible line in its center called an axis. That line runs between the North Pole and South Pole, and it takes 24 hours to make one full turn on the axis.
The reason why the Earth spins is because it formed from a cloud of gas and dust that collapsed under its own gravity. This created a spin that was similar to what figure skaters do when they pull in their arms and spin faster.
That spin sped up as the gas and dust clumped together to form planets, and it stayed that way until the solar system was formed about 4.6 billion years ago. That was when the gas and dust began to clump together even more closely, like a rock coming together to form an ice cream cone or a ballerina’s arm forming her twirl.
And since those clumps of dust and gas were already spinning in a circle, the planets that grew out of them picked up on that spin and began to spin too.
Just as a spinning top will keep spinning forever as long as you add or take away energy, so too will the Earth. The only thing that can slow or stop it is something else, like gravity or friction.
If there were a force that made the Earth stop spinning, then it would be because we could no longer get enough energy out of the ground to continue the spin. But it is not that simple, because the Earth has a magnetic field with North and South Poles.
There is also a Coriolis effect that causes falling bodies and projectiles to veer slightly eastward in the opposite direction of their path. This is a very subtle effect that most people don’t notice, but it is important for understanding why the Earth rotates and how it makes day and night.
The rate of acceleration that the Earth has in its rotation is largely determined by the tides. The tides are constantly changing, and they affect the Earth’s rotation by causing it to shave off fractions of a second. That’s what is causing more record-short days, and it’s only going to get worse as time goes on.