why does the earth spin around the sun
Why do the planets rotate around the Sun? First, please note that "rotate" actually is used to describe an celestial body's spin, and "revolve" is used to describe its orbital motion. For example, the Earth completes one rotation about its axis about every 24 hours, but it completes one revolution around the Sun about every 365 days. Anyway, the basic reason why the planets revolve around, or, the Sun, is that the
of the Sun keeps them in their orbits. Just as the Moon orbits the Earth because of the pull of Earth's gravity, the Earth orbits the Sun because of the pull of the Sun's gravity. Why, then, does it travel in an around the Sun, rather than just getting pulled in all the way? This happens because the Earth has a velocity in the direction perpendicular to the force of the Sun's pull. If the Sun weren't there, the Earth would travel in a straight line. But the gravity of the Sun alters its course, causing it to travel around the Sun, in a shape very near to a circle. This is a little hard to visualize, so let me give you an example of how to visualize an object in orbit around the Earth, and it's analogous to what happens with the Earth and the Sun. Imagine Superman is standing on Mt. Everest holding a football. He throws it as hard as he can, which is incredibly hard because he's Superman.
Just like if you threw a football, eventually it will fall back down and hit the ground. But because he threw it so hard, it goes past the horizon before it can fall. And because the Earth is curved, it just keeps on going, constantly "falling," but not hitting the ground because the ground curves away before it can. Eventually the football will come around and smack Superman in the back of the head, which of course won't hurt him at all because he's Superman. That is how orbits work, but objects like spaceships and moons are much farther from the Earth than the football that Superman threw. (We're ignoring air resistance with the football example; actual spacecraft must be well above most of a planet's atmosphere, or air resistance will cause them to spiral downward and eventually crash into the planet's surface. ) This same situation can be applied to the Earth orbiting the Sun - except now Superman is standing on the Sun (which he can do because he's Superman) and he throws the Earth. The next question, then, is how did Earth get that velocity, since in real life there's no Superman throwing it. For that, you need to go way back to. This page was last updated on January 31, 2016. Earth spins on its axis once in every 24-hour day. At EarthБs equator, the speed of EarthБs spin is about 1,000 miles per hour (1,600 kph).
The day-night has carried you around in a grand circle under the stars every day of your life, and yet you donБt feel Earth spinning. Why not? ItБs because you and everything else Б including EarthБs oceans and atmosphere Б are spinning along with the Earth at the same constant speed. ItБs only if Earth stopped spinning, suddenly, that weБd feel it. Then it would be a feeling similar to riding along in a fast car, and having someone slam on the brakes! Think about riding in a car or flying in a plane. As long as the ride is going smoothly, you can almost convince yourself youБre not moving. A jumbo jet flies at about 500 miles per hour (about 800 km per hour), or about half as fast as the Earth spins at its equator. But, while youБre riding on that jet, if you close your eyes, you donБt feel like youБre moving at all. And when the flight attendant comes by and pours coffee into your cup, the coffee doesnБt fly to the back of the plane. ThatБs because the coffee, the cup and you are all moving at the same rate as the plane. Now think about what would happen if the car or plane wasnБt moving at a constant rate, but instead speeding up and slowing down. Then, when the flight attendant poured your coffee Б look out! Earth is moving at a fixed rate, and weБre all moving along with it, and thatБs why we donБt feel EarthБs spin.
If EarthБs spin were suddenly to speed up or slow down, you would definitely feel it. The constant spin of the Earth had our ancestors pretty confused about the true nature of the cosmos. They noticed that the stars, and the sun and the moon, all appeared to move above the Earth. Because they couldnБt feel Earth move, they logically interpreted this observation to mean that Earth was stationary and Бthe heavensБ moved above us. With the notable exception of the early Greek scientist Aristarchus, who first proposed a heliocentric (sun-centered) model of the universe hundreds of years B. C. E. , the worldБs great thinkers upheld the geocentric (Earth-centered) idea of the cosmos for many centuries. It wasnБt until the 16th Century that the heliocentric model of Copernicus began to be discussed and understood. While not without errors, CopernicusБ model eventually convinced the world that Earth spun on its axis beneath the stars Б and also moved in orbit around the sun. Bottom line: Why donБt we feel Earth rotating, or spinning, on its axis? ItБs because Earth spins steadily Б and moves at a constant rate in orbit around the sun Б carrying you as a passenger right along with it.
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