On Jan 9, 2012, at 11:31 PM, Rob Seaman wrote: > As you point out, this is an approximation not a definition of a fundamental > concept. The synodic day is good from now until the Earth melts. It is the > difference between the rotational period of a planet and its day. See, for > instance: http://cseligman.com/text/sky/rotationvsday.htm
Actually, it is a more fundamental concept because it doesn't depend on the earth. Your definition of the day depends on what the earth does. Mine is just an extension of the fundamental SI second and needn't have earth's rotation to guide it. It can be recovered from the beat frequency and pattern of pulsars and the local pattern of stars in the sky. With the earth rotation, hundreds thousands of years from now, you can't know how many days have been lost due to the slowing of the earth, but you can estimate the elapsed time. You can also know the time of day, but that's less relevant. As a unit of measure of time, number of rotations of earth is convenient, but hardly fundamental. Would time still pass if earth ceased to exist? Yes. Would earth days accumulate still? No. Seems like a rather silly thing to base a fundamental standard on. Almost as silly as basic your standard length on a hunk of platinum sitting in a vault in Paris. Like I said, it is a belief that it is right. It is an opinion about what to base things on, and one's view of the esthetics of your definition. It is not inherently a fundamental concept. Warner _______________________________________________ LEAPSECS mailing list [email protected] http://six.pairlist.net/mailman/listinfo/leapsecs
