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How Fast Does the Earth Rotate?


This article originally appeared in 2009, but I’ve updated it and added this video.

The ground feels firm and solid beneath your feet. Of course, the Earth is rotating, turning once on its axis every day. Fortunately gravity keeps you firmly attached to the planet, and because of momentum, you don’t feel the movement – the same way you don’t feel the speed of a car going down the highway. But how fast does the Earth rotate?

You might be surprised to know that a spot on the surface of the Earth is moving at 1675 km/h or 465 meters/second. That’s 1,040 miles/hour. Just think, for every second, you’re moving almost half a kilometer through space, and you don’t even feel it.

Want to do the calculation for yourself? The Earth’s circumference at the equator is 40,075 km. And the length of time the Earth takes to complete one full turn on its axis is 23.93 hours.

Wait, 23.93 hours? Isn’t a day 24 hours? Astronomers calculate a day in two ways. There’s the amount of time it takes for the Earth to complete one full rotation on its axis, compared to the background stars. Imagine you were looking down at the Earth from above the North Pole. You’d see the Earth turn once completely in 23 hours and 56 minutes. Astronomers call this a sidereal day.

And then there’s the time it takes for the Sun to return to the same spot in the sky. Since the Earth is orbiting the Sun, we actually need an extra 4 minutes each day to return the Sun to the same spot. Astronomers call this a solar day.

Then we divide the length of a day into the distance a point on the equator travels in that period: 40,075 km/23.93 hours = 1,675 km/hour, 465 meters/second.

The speed of the Earth’s rotation changes as you go North or South away from the equator. Finally, when you reach one of the Earth’s poles, you’re taking a whole day to just turn once in place – that’s not very fast.

Because you’re spinning around and around on the Earth, there’s a force that wants to spin you off into space; like when you spin a weight on a string. But don’t worry, that force isn’t very strong, and it’s totally overwhelmed by the force of gravity holding you down. The force that wants to throw you into space is only 0.3% the force of gravity. In other words, if the Earth wasn’t spinning, you would weigh 0.3% more than you do right now.

Space agencies take advantage of the higher velocities at the Earth’s equator to launch their rockets into space. By launching their rockets from the equator, they can use less fuel, or launch more payload with the same amount of fuel. As it launches, the rocket is already going 1,675 km/hour. That makes it easier to reach the 28,000 km/hour orbital velocity; or even faster to reach geosynchronous orbit.

We have written many articles about the Earth for Universe Today. Here’s an article about why the Earth rotates.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

References:
NASA Space Place
NASA Solar System Exploration: Earth

About 

Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

Comments on this entry are closed.

  • Planemo May 20, 2013, 10:40 PM

    Common sense says 24 hr per day = 1,000MPH. It is actually 1040MPH. I was off by 40MPH. I got to get it adjusted. ;~)

    • Torbjörn Larsson May 21, 2013, 9:09 PM

      Wait, what!? Common sense has nothing to do with science, science has nothing to do with miles, and statute miles has nothing to do with common sense.

      Nautical miles however do have a correlation between units and geography. But nautical miles have nothing to do with land miles (statute miles).

      • Planemo May 21, 2013, 10:14 PM

        Wait who? What when? Say what?

        I was not being technical. I was jokingly playing with the numbers via 24 hrs in a day vs approximately 24,000 miles wide at earths equator. Actually I believe it is 24,925 miles around at the equator. Notice I said, “I was off by 40 miles” and “close enough for me”. A selfrighteous claim. Get it now?

        The MPH earth spinning and the speed the earth is orbiting around or star is accurate. So much for your common sense to detect my selfrighteous claim. Yet, I cannot blame you. My fault. Nautical miles was my way of life for many many years. I am(was)a seasonal fisherman from the Gulf of Maine, George’s Banks, to Florida and many many ports of fishing cities and villages.

  • danangel May 21, 2013, 2:18 AM

    ” Just think, for every second, you’re moving almost half a kilometer through space, and you don’t even feel it.”

    If we add that to the speed of our revolution around the sun, the speed of the sun in orbit around the galactic center, and the motion of the Milky Way through the Universe, it is probably much faster still.

  • Kevin Frushour May 21, 2013, 3:10 AM

    The Earth is calm and quiet? You haven’t been around my kids.

  • Torbjörn Larsson May 21, 2013, 9:28 PM

    The situation is a nice illustration of classical mechanics:

    Fortunately gravity keeps you firmly attached to the planet, and because of momentum, you don’t feel the movement

    That isn’t momentum though, which is p = mv.

    The reason you don’t feel movement is simply because of balance of forces between gravity acting as centripetal force and the Earth pushing upward on you.*

    there’s a force that wants to spin you off into space;

    That is momentum and technically speaking it isn’t a force, no acceleration as in F = ma. Or more generally no change in F = d(p)/dt = d(mv)/dt – unless you throw up as gravity turns off and you sail away following the momentum the rotating Earth has imparted on you.

    * The actual physics is quite different, as per general relativity. But we are illustrating classical mechanics.

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