hstrop (11/05/82)
For those people who couldn't live without this info: one day(earth rotation) = 23 hours, 56 minutes, and 4 seconds Nothing for the guy on the street to worry about, but now you know why the days seem shorter than when you were a kid.
z (11/05/82)
From decvax!harpo!eagle!mhuxt!hstrop Thu Nov 4 18:45:52 1982 Subject: length of day Newsgroups: net.unix-wizards For those people who couldn't live without this info: one day(earth rotation) = 23 hours, 56 minutes, and 4 seconds Nothing for the guy on the street to worry about, but now you know why the days seem shorter than when you were a kid. How could this be true? If this were so, after about 100 days everybody's clock would be six hours off, the sun would be rising at midnight, etc. Actually, the earth's rotation is somewhat variable, but it's so close to 24 hours that over the period of a year, clocks are off by only a second or two. To compensate for this, a "leap second" is added or subtracted at the end of June and the end of December, when necessary.
thomas (11/05/82)
Once and for all: The 'sidereal day' is 23 hours, 56 minutes, and 4 seconds. This is the period of the Earth's rotation with respect to the Universe (whatever that means). The 'mean solar day' is 24 hours exactly (with the exception of those leap seconds, which get stuck in because the second is defined relative to the mean solar day of 1900, and the day is slowly lengthening). Is that clear? =Spencer
djb (11/08/82)
It's true nonetheless - a single rotation of Mother Earth takes 23 hours, 56 minutes and 4 seconds. How come our clocks stay close, and the Sun doesn't rise at midnight? What we mean by period of rotation is the time it takes to rotate through a full 360 degrees. Go outside and look up. After 23h 56m 4s, you've been rotated back and are facing outward into the universe in the same direction. While the Earth was rotating, however, it was also orbiting the Sun, processing around the Sun a tiny bit each day. (Moving almost a degree in its orbit while you were being rotated). This movement leaves the Sun slightly behind (in an angular sense). It takes almost four more minutes of rotating to compensate for this incremental daily precession of the Sun. This combination (23h 56m 4s rotation period plus ~4 minutes extra to return the Sun to its position of the day before) produces a 24 hour solar day. Well almost. There's enough error there to require an additional day be inserted into our calendar every four years. David Bryant cbosg!djb
colbert (11/10/82)
Rotation of the day with respect to an inertial reference frame or to the sun? I believe that 23 hours 56 minutes is with respect to an inertial frame (actualy to some stars drifting in space), and 24 hours is measured against the relative position of the sun. Remember that the Earth is moving in it's orbit about the sun, so the sun has shifted it's position relative to us. Remember this next time you are trying to land a spaceship with it's autopilot blown away. Charles Colbert pyuxjj!colbert pyuxww!colbert