Rotation

Recall the rotation period of the Earth (23 hours 56 minutes) and the time to rotate through 1 degree (4 minutes)

The Earth takes 23 hours and 56 minutes to rotate once. This is known as a Sidereal Day; visit the Day page to find out more.

If it takes approximately 24 hours to travel 360° then we can make an approximation that it travels 15° in 1 hour and also 1° in 4 minutes.

Why do we see the Sun rise in one place and set in another?

Imagine you are facing south. Now think of a ball moving from left to right (east to west). This is the direction the Sun appears to move in the sky.

We know the Earth goes around the Sun and not the other way around.

Let us imagine the ball hangs in the air. How would you have to move your head to ‘see’ the ball moving from east to west? You would have to move from west to east.

If you hovered above the Earth, above the North Pole, you would see the Earth move counter clockwise.



Questions

Image

Look at the picture. If you lived in Plymouth, what is the approx. difference in time that you would see the sunrise compared with your friend in London?

Will the answer be earlier or later?

1° = 4 minutes
4 x 4 = 16
Answer is later as the Sun rises first in the east.

Animation

Summary

1 Sidereal Day = 23h 56m
15° = 1 hour
1° = 4 minutes

Links

Windows to the Universe Earth's rotation