How Fast Does the Earth Rotate?

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:

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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.

[frasercain]

See, some like longer, more in-depth stuff, and other people prefer the shorter stuff. I'm happy to experiment with both.

[frasercain]

We have a mountain of podcasts recorded and flowing out into the feed. We were just waiting on our editor and trying to fit things around our busy schedules.

[JamesHaney]

"We're fallin' through space, you and me, clingin' to the skin of this tiny little world, and if we let go...." --The Ninth Doctor from "Rose".

[frasercain]

I'm glad you're enjoying them. Some people really love the Virtual Star Parties, and they're fun and meaningful. Others prefer the shorter style of these. I really just want to keep experimenting.

[finlarg]

Long or short, it's all good! I tend to watch the shorter videos, but listen to the podcasts at work. They really help to clarify my understanding of astronomy. Keep up the good work!

[frasercain]

Thanks for catching that, I've put in an annotation to fix it.

[frasercain]

I'm using an iPad attached to my Tripod. It's actually just below the camera.

[shelloz]

Why does the speed of rotation slow down as you approach the poles? So the fastest rotation occurs at the equator, and slows as you further yourself from the equator in either direction?

[finlarg]

If you're on the equator, you're moving at about 1 thousand MPH, relative to the centre of the earth. Fraser didn't cover it in this video, but we're also moving at about 66 thousand MPH, relative to the sun - wherever you're standing on the earth. It all depends on your frame of reference!

[JoelZucker]

You shouldn't say, "Hurtling through space at 465 meters/hour..." as the reference to space changes your relative viewpoint as to overall speed. If you are going to bring the perspective of space into the picture, then you need to determine the relative speed of the Earth with respect to the sun (if that is going to be your basis for speed calculation). Depending on your position in your rotation of the Earth, you can either add, or subtract, your relative rotational ... I've run out of chars.

[Ramiromasters]

So what happens if you fly from Canada to Central America?
Wouldn't you have to accelerate quite a lot to catch up to that side's speed of rotation?

[jaimiebigelow]

Thanks for the video ~ so articulately explained and thus easy to understand and the notes in the upper right are absolutely hilarious!

[frasercain]

Right, so "how fast does the Earth revolve around the Sun is a completely different question. I'm thinking of doing another episode called, "How fast are you moving when you're standing still", and look at the perspective from different places in the Universe.

[SuperGuitarman]

You just proved that we are not spinning around the sun. Thank you, I will use this.

[frasercain]

We thought about that, we'll definitely experiment more with different styles.

[manikyajoshi]

1:37 circumference of earth is 40, 075 km

[PrestonGarveyofthesettlements]

You know, I think that flat earthers are forgetting one thing in regards to why they don't notice the rotation: the size of the planet. Take a quarter, spin it 25mph, and then take something bigger like a wheel, and spin that at 25mph and watch how a wheel looks like it's rotating slower.

Also, how would seasons work on a flat Earth?

[jimf]

All this is making my head hurt, so I'm going to bed, good night !

[konasquareheed]

Hi Fraser i was just wondering why there has been a lack of podcasts on astronomy cast but you have put new youtube episodes up i miss the podcasts will you be uploading anymore soon (not the weekly hangouts) i need more info from you and Pamela!!!

[mecchie]

love the text comment bits....especially the gollum-esque one! Wondering how big your cue cards are? ;-) That is one of the things I hate as an amateur astronomer in the public..trying to remember all those damn numbers....