How Fast Does Earth Spin? Why Does Earth Spin?

(Last Updated On: April 4, 2019)
How Fast Does Earth Spin? Why Does Earth Spin?

How Fast Does Earth Spin?

The Earth’s characteristic 24-hour rotation period is what is responsible for what we know as night and day. In fact, the comfortable temperature variation between warm days and cool nights is one of the things that makes Earth so ideal for hosting life.

So, how fast does Earth spin? The actual speed of the Earth’s rotation is about 1,000 miles per hour as measured from the equator, so it might seem strange that people can’t actually feel the Earth spin. The reason is essential, that we are just used to it. Since the Earth spins at a steady rate, we don’t notice it spinning. However, if the Earth’s rotation was to suddenly speed up, slow down, or stop, it would be very noticeable indeed!

The Earth, like most other planets in the solar system, rotates in a counter-clockwise direction. There are a couple of exceptions to this rule, but we’ll get into that later.

Why Does Earth Spin?

Essentially, the Earth spins because there is no force out there in the solar system to stop it from spinning.

It all goes back to the way that the Earth was formed in the first place. The solar system first began to take shape about 4.6 billion years ago. At the time, it was all nothing more than a massive cloud of dust and hydrogen gas. The force of some major event, like a supernova, caused the gas to begin to collapse inward, and eventually, this cloud flattened into a disk shape and began to slowly spin, with the Sun gradually forming as a lump in the center of the spiral.

This spiral pattern was formed by a physical law referred to as the “conservation of angular momentum,” which is a result of gravity pulling particles together, and the particles trying to even out their own natural momentum to match the other particles. Faster moving particles produce excess energy that is used to propel a spinning motion as the particles get closer and closer together. The closer they get, the more speed they produce. This is why people pull their arms closer to their bodies to create a spinning motion.

Bit by bit, smaller spirals began to form within the larger one, clumping the dust and hydrogen into what we know today as the planets of the solar system. Most planets adopted the same rotation of the larger spinning solar system they belong to. If a smaller planet fell into the orbit of a larger one, the smaller one would succumb to the more powerful orbit and become a moon.

Earth and the Moon

Sometimes moons were formed when planets bumped into each other and a chunk would break off and remain stuck in the larger planet’s orbit. In fact, many scientists believe that this is how Earth ended up with its moon, probably during a collision with Mars. This theory is referred to as the Giant Impact Hypothesis.

The Earth’s rotation continues to have an interesting reciprocal relationship with the Moon. As the Earth spins nearby, the Moon’s gravity affects the ocean tides, while the friction created by the tides affects the Earth’s rotation and slows it ever so slightly. This means that as we age, the days don’t get shorter, they actually get longer. Not much longer though. The difference is only about 2 milliseconds every 100 years.

So What About the Other Planets in the Solar System?

All planets in the solar system spin, just like Earth. However, they don’t spin at the same rate. Each planet in the solar system has its own trademark rate of rotation. For example, on Venus, one rotation takes 243 days on Earth.

That’s not the only stand-out feature of Venus’s rotation though. In addition to rotating very slowly, relatively speaking, the “planet of love” also rotates clockwise, in the opposite direction of its own orbit. The same is true for Uranus. This unusual rotation pattern is referred to as a “retrograde rotation.” Scientists aren’t exactly sure why these planets rotate opposite of the general direction of the solar system, but the most prominent theory is that at some point they were struck by an object large enough to actually reverse their rotation.

Did you like this post? Check out these other Space-themed articles from the Sporcle blog.

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