Since someone mentioned "space" earlier in this thread:
With the universe, or a distant star as a reference, the earth doesn't rotate one revolution in 24 hrs, it actually goes a little further (1/365th of a rotation).
Since earth rotates counterclockwise around itself, while travelling counterclockwise around the sun, in one year, it'll have made an extra revolution. You can easily visualize this if you imagine a year only having 4 days, the earth moving one fourth of the way around the sun every day.
The earth's true rotation period (w.r.t. the background stars) is actually 23 hour 56 minutes. This is called the "sidereal" day.
Sidereal time - Wikipedia, the free encyclopedia