|Moche, Dinah. Astronomy. 4th ed. Wiley, 1993: 24.||"23 hours, 56 minutes, 4 seconds long"||86,164 s|
|"Earth." Microsoft Encarta 97 Encyclopedia. Microsoft, 1996.||"… the earth rotates on its axis every 23 hours, 56 minutes and 4.1 seconds based on the solar year."||86,164.1 s|
|Daily, Robert. Earth. USA, 1994: 20.||"… it takes earth 23 hours, 56 minutes and 4.09 seconds, a period of time we call a day."||86,164.09 s|
|"Earth." Encyclopedia Britannica. Chicago: Encyclopedia Britannica, 1998: 320.||"… the earth spins on its axis and rotates completely once every 23 hours, 56 minutes and 4 second."||86,164 s|
|Earth's Rotation. Liftoff to Space Exploration. NASA. Marshall Space Flight Center.||"The actual value is 23 hours, 56 minutes and 4 seconds."||86,164 s|
The earth is the third planet from the sun. To most people the period of rotation of the earth is 24 hours, but the actual value is 23 hours 56 minutes and 4 seconds. This happens because a solar day is longer than a sidereal day. While the earth rotates, it also moves around the sun in the interval from one day to another. The Earth completes a little more than one turn in space each solar day. Which is why the period of rotation is not 24 hours.
The earth spins around its axis. This spinning makes the sun appear to move from east to west across the sky. It takes 23 hours 56 minutes and 4 seconds for the earth to make a complete rotation about its axis. It is also the length of a sidereal day -- the time it takes the earth to rotate 360°. A sidereal day could be measured using fixed stars.
In conclusion the actual period of rotation of the earth is 23 hours 56 minutes and 4 seconds or 86,164 seconds.
Limin Chen (Jenny) -- 1999