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Re: Beginner moonrise and set question
From: Frank Reed CT
Date: 2004 Sep 24, 21:54 EDT
From: Frank Reed CT
Date: 2004 Sep 24, 21:54 EDT
Previously posted:
"Actually, 24h rotation of earth is also slightly MORE than 360 deg arising from the earths orbit around the sun"
And Bill asked:
"Relative to what? Agreed the Earth has to over-rotate relative to the stars
for the Sun to be close to the meridian passage at noon"
Relative to inertial frames of reference. It might seem as if "it's all relative" but the Earth's TRUE rotation rate has an absolute meaning and it's close to that 23h 56m that's been posted previously. It's known as the sidereal rotation, but this rate can be detected without reference to the stars. A Foucault pendulum will show it. Another trick, less practical but interesting in principle, would be to place a basin of Mercury on a turntable at the North Pole. If you rotate the turntable clockwise OR counter-clockwise, the Mercury will form a parabolic "bowl". The surface of the Mercury in the bowl will be flat (ignoring curvature of the Earth's surface) only if it is rotating slowly clockwise as seen from above at a rate of one rotation in 23 hours and 56 minutes.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
"Actually, 24h rotation of earth is also slightly MORE than 360 deg arising from the earths orbit around the sun"
And Bill asked:
"Relative to what? Agreed the Earth has to over-rotate relative to the stars
for the Sun to be close to the meridian passage at noon"
Relative to inertial frames of reference. It might seem as if "it's all relative" but the Earth's TRUE rotation rate has an absolute meaning and it's close to that 23h 56m that's been posted previously. It's known as the sidereal rotation, but this rate can be detected without reference to the stars. A Foucault pendulum will show it. Another trick, less practical but interesting in principle, would be to place a basin of Mercury on a turntable at the North Pole. If you rotate the turntable clockwise OR counter-clockwise, the Mercury will form a parabolic "bowl". The surface of the Mercury in the bowl will be flat (ignoring curvature of the Earth's surface) only if it is rotating slowly clockwise as seen from above at a rate of one rotation in 23 hours and 56 minutes.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
