Planetary Science
Time

How many degrees does earth rotate per day?

Answer

Wiki User
01/18/2009

You are a clever questioner, indeed. You have asked a subtle and interesting question. You probably know that there are at least two distinct answers to the question, because there are two different kinds of day. The sidereal day is the period during which earth rotates 360 degrees relative to the distant stars (not the sun). If you were far above the solar system looking down on earth from the north, you would see that earth rotates a full 360 degrees relative to the stars, but still has to rotate a little more to reach the starting point relative to the sun, because we orbit the sun, this complicates things a little bit. So in a sidereal day, the earth rotates exactly 360 degrees, but this day lasts only 23 hours 56 minutes and 4.1 seconds, roughly. The synodic day is the period during which earth rotates one time relative to the sun. This rotation will be slightly more than 360 degrees, because as explained above the earth has to rotate a little extra (beyond a full 360 degrees) in order to reach the starting point relative to the sun. This is the day as we typically experience it. So if you are asking about the earth's rotation during a synodic day, the rotation is closer to an average of 360.9856 degrees per day. Another way to look at this is to consider the earth's coordinate system. There are 360 degrees of longitude. It is possible to consider the earth's degrees of longitude as the basis of your measurement, so that you can say the earth rotates 360 degrees of longitude relative to the sun on average each day, even though the absolute rotation of the earth is closer to 360.9856 degrees on average.