Earth's rotation
We have discovered the Earth does not always take exactly 24 hours to for one "exact" rotation.
(1) How do scientists know when the earth has made an exact 360 degree rotation? We can't drive a stake and watch for it to come around again, can we?
(2) The exact rotation can be a random plus or minus a few milliseconds. What have scientists said causes this varation?
(1) How do scientists know when the earth has made an exact 360 degree rotation? We can't drive a stake and watch for it to come around again, can we?
(2) The exact rotation can be a random plus or minus a few milliseconds. What have scientists said causes this varation?
posted by Ragknot at
11:30 AM
8 Comments:
These are just guesses, I'm not a physicist.
1) They measure the degree of the Earth towards certain stars outside of our solar system?
2) The gravity of the moon?
This post has been removed by the author.
mo's certainly right about the fixed stars being used to define the reference system - i.e. the fixed stars. The associated measurement system is known as sidereal time.
I guess that the moon should go round smoothly enough that short variation of a millisec or so might be achievable, using the Moon's orbit as a reference.
I guess that the Moon's disturbance of the Earth's innards might be responsible for the short and long term changes of the Earth's spin rate. It's not something crazy like the effects of human traffic is it?
Ooop. I misread the question. I thought the millisec variations were on a daily basis - that did surprise me. I think that the Moon is still the main culprit.
Scientist use a far, far away pulsar and two very distant radar telescopes. The pulse read by the two telescope vary slightly because
different distance from the pulsar. When the pulses become in synce, the two telescopes are the same distance from the pulsar.
Picture the telescopes at positions 2 o'clock and 10 o'clock
on the earth surface, then the pulsar would be in the 12 oclock direction. About 24 hours later, when the pulse syncs up again, it has been 360 degrees.
This, I thought was strange, the millisecond variatitions are caused by winds blowing on the mountains and surface.
Thanks for that. I didn't know either of those things.
I just saw a show titled "What time is it?" today on the History, or maybe the Discovery channel. I recorded it last week. Very good.
I would of guessed seasonal freezing and melting of polar ice.
Zach.
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