Most people know Earth completely rotates once every 24 hours, giving us day and night, but have you ever wondered how fast it actually spins?
I guess since I’ve never felt Earth’s rotation, I’ve always assumed it rotated at a fairly slow rate. I mean, the sun doesn’t seem to speed across the sky during the day and, more importantly, we aren’t getting flung off into outer space, so I decided to do some simple math and found out that Earth is actually spinning really fast!
How to calculate the rotational speed of Earth
So how does one calculate the speed at which the Earth rotates? It’s very simple, you just need to divide the circumference of Earth by the number of hours in a day and voila! Of course, even though I knew there were roughly 24 hours in a day, I had no idea what the circumference of Earth was. After some quick research, though, I found out the circumference of Earth at the equator is about 24,900 miles, so if we divide that number by 24 hours, we get…
Wait a second, are there really 24 hours in a day? While I was looking into all of this, I ran across some information about sidereal days and solar days, which are two different methods for determining the length of a day. Although I was aware of the concept of a solar day, I didn’t know that’s what it was called, and had never even heard of a sidereal day, so here’s what they are in a nutshell.
A sidereal day is the time it takes Earth to rotate once relative to a fixed star in the sky. For example, if you were to aim a telescope at a star and wait until that same star came back into view, it would take a sidereal day, or just about 23 hours, 56 minutes, and 4 seconds.
A solar day is similar, but it is the time it takes Earth to rotate once relative to the position of the sun. If you were to aim that same telescope at the sun, with a solar filter of course, and wait until it came back into view, it would take a solar day, or 4 minutes longer than a sidereal day, or 24 hours.
Calculating Earth’s rotational speed
Now that we know a couple of ways to measure the length of a day, we’re going to keep things simple and stick with the original idea of 24 hours, or a solar day, so let’s go back to the original equation. If we take the circumference of Earth (24,900 miles) and divide it by the number of hours in a day (24 hours) we get approximately 1,038—or for simplicity’s sake, 1,000. That’s 1,000 miles per hour!
Because the speed of rotation changes the further north or south you travel from the equator; If you were to stand at the North or South Pole facing one direction, it would take a mind-numbing 24 hours for you to rotate back to your starting position. Slow motion anyone?
Just how fast is 1,000 miles per hour?
It’s pretty hard for most of us to comprehend exactly how fast 1,038 miles per hour is, so here are some common speed comparisons to help us get a good sense of its speed. Keep in mind, however, the following speeds on this list are averages and approximates and may not accurately represent actual speeds.
Did you know?
- The average walking speed is 3.1 mph
- The average cycling speed is 9.6–25 mph
- The average driving speed is 70 mph
- A cheetah can run at speeds up to 75 mph
- The average high-speed train speed is 124-155 mph
- The average airplane speed is 546–575 mph
- The speed of sound (Mach 1) is 767 mph
- Earth rotates at 1,000 mph
- Mach 2 is 1,534 mph
- The average bullet speed is 1,700 mph
- The speed of light is approximately 671,000,000 mph
I have to admit, I was pretty amazed when I first figured all of this out. Aside from air travel, the fastest I’ve ever gone on land is just over 100 mph, so it’s kind of amazing to imagine that Earth is spinning ten times faster than that! Just for fun, try to imagine what it would be like hanging on to a rope that’s dangling from outer space above Earth’s surface while all of the continents and oceans speed beneath your feet. Oh, and one last thing, if you happen to be hanging on to that rope near the equator, watch out for Mount Chimborazo—the highest spot on Earth!