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SW-User
Well,technically there鈥檚 no such thing as a day. Humans came up with the idea to try and measure time
DrWatson 路 70-79, M
@SW-User I'm not sure what you mean. I agree that our units of time are somewhat arbitrary (although it works out well for 24 time zones to divide the 360 degrees around the equator into nice 15 degree intervals). But the earth does rotate, and it seems to me that counting the number of rotations is based on something objective.
A solar day, 24 hours, is the amount of time for a point on the Earth to return to the same position it currently is in, relative to the sun. That sounds like something real to me.
A more meaningful measure is the sidereal day, of 23 hours, 56 minutes, and 4.1 seconds, which is the actual amount of time for one full rotation. (The difference is due to the fact that as the earth rotates, the sun is moving, so the solar day is measured relative to a moving target. After the earth has undergone one rotation, it has to rotate a little more, for about 4 minutes, to catch up to the sun and complete a solar day.)
I agree that humans came up with the idea to pay attention to all of this, but I don't agree that the notion of the earth's rotation was a human idea. The way I see it, these two notions of a "day" are objectively there -- we can either use what nature gave us or not. But a day is a real thing.
A solar day, 24 hours, is the amount of time for a point on the Earth to return to the same position it currently is in, relative to the sun. That sounds like something real to me.
A more meaningful measure is the sidereal day, of 23 hours, 56 minutes, and 4.1 seconds, which is the actual amount of time for one full rotation. (The difference is due to the fact that as the earth rotates, the sun is moving, so the solar day is measured relative to a moving target. After the earth has undergone one rotation, it has to rotate a little more, for about 4 minutes, to catch up to the sun and complete a solar day.)
I agree that humans came up with the idea to pay attention to all of this, but I don't agree that the notion of the earth's rotation was a human idea. The way I see it, these two notions of a "day" are objectively there -- we can either use what nature gave us or not. But a day is a real thing.
ArishMell 路 70-79, M
@DrWatson Yes - a good point.
A very simple demonstration of the day's reality even if the division is artificial, is given by the humble sundial.
Similarly with the Year of course - whose sneaky extra quarter-day created havoc for people trying to correlate the real year with their calendars, for centuries until it was discovered.
Didn't someome (possibly France's post-Revolutionary government?) once consider a decimal day or decimal hours? I vaguely recollect reading something to that effect. They did proposal dividing the circle into 400 degrees, making the right-angle = 100潞. Proposals no doubt by people who never have to use such things for practical purposes themselves.
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"Square Hours"... Well, October has 31 Square Days. It must have because my wall-calendar grid shows them.....
A very simple demonstration of the day's reality even if the division is artificial, is given by the humble sundial.
Similarly with the Year of course - whose sneaky extra quarter-day created havoc for people trying to correlate the real year with their calendars, for centuries until it was discovered.
Didn't someome (possibly France's post-Revolutionary government?) once consider a decimal day or decimal hours? I vaguely recollect reading something to that effect. They did proposal dividing the circle into 400 degrees, making the right-angle = 100潞. Proposals no doubt by people who never have to use such things for practical purposes themselves.
'
"Square Hours"... Well, October has 31 Square Days. It must have because my wall-calendar grid shows them.....