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How Fast Does the Earth Rotate?

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Published on May 20, 2013

In this short video, Universe Today publisher Fraser Cain does the math to help you understand just how fast you're spinning in space right now, and how you'd actually gain a little weight if the Earth stopped spinning.

Based on this article from Universe Today:
http://www.universetoday.com/26623/ho...

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The Earth feels firm and solid beneath your feet. Everything's calm and quiet. Right?

We know the planet is rapidly spinning on its axis completing one full rotation every day.

As we're gravitationally bound to the planet, and hurtling around in space, right along with it.

We follow a circular path around the Earth at hundreds of kilometers per second.

So, just how fast does does it spin, and how fast are we rotating around on the surface?

Before we can talk speed, I've got to clarify how long a day is, it gets a little sticky.

We count a day as twenty-four hours.

This is the length of time it takes for the Sun to return to the exact same spot in the sky as it was in the day before.

Astronomers call this a solar day. Here's where it gets a little complicated.

As we're taking a full year to go around the Sun, and changing our relative position to our star, we have to add about four minutes every day to nudge the Sun back into the same spot.

Which means if you look down at the Earth and watch it turn one complete rotation on its axis, you'd count twenty-three-point-nine-three hours.

This is what's known as a sidereal day and is a more accurate measurement of the planet's rotation. This is the amount of time we're going to use to calculate the speed the Earth turns at.

Let's assume that you're standing on the equator, the halfway point between the north and south pole.

Over the course of a sidereal day you'll travel along the entire circumference of the Earth, and end back to your starting point.

We know the circumference of the Earth is fourty-thousand-and-seventy-five kilometers.

Divide twenty-three-point-nine-three hours into the circumference and you get
one-thousand-six-hundred-and-seventy-five kilometers per hour, or four-hundred-and-sixty-five meters per second.

Every second that goes by, you've hurtled almost half a kilometer through space,
and you didn't even break a sweat.

This spinning is even causing you to lift off the Earth a little bit, like when you spin a weight on a string.

That lifting force is about zero-point-three-percent of the force of gravity pulling you down.

If the Earth wasn't spinning, you'd weigh zero-point-three-percent more than you do now.

As you travel towards the poles, your speed of rotation slows down.

Just imagine if you were standing straight upright on the North Pole, lining your own axis up with the earth.

It would take you a whole day to turn around once, which is pretty slow even by sloth standards.


Our space agencies take advantage of the Earth's rotation to launch rockets.

The closer you are to the equator, the less fuel you need to get into orbit, or the heavier payloads you can carry.

That's why Cape Canaveral in Florida is a great place to launch rockets.

Some clever people created Sea Launch, which blasts rockets off from an ocean platform, right at the equator.

Which is even better at maximizing your launch benefits of planetary rotation.

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