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
I also appreciated Markus's suggestion. Rob -- On Jan 9, 2012, at 11:18 PM, Warner Losh wrote: > > On Jan 9, 2012, at 11:02 PM, Rob Seaman wrote: >> Warner Losh wrote: >>> It is only one possible definition, not the only one. That makes it a >>> belief, not a mathematical identity. >> >> Alternate definition? > > A SI second is defined by BIPM. > > Everybody knows that minutes have 60 seconds, hours have 60 minutes and days > have 24 hours. Make that with SI seconds and you have the basis of the > definition of a day: 86400 SI seconds. This is the "elapsed time" definition > of a day, not an astronomical definition. It is an approximation of the > astronomical definition, much in the same way that an SI second is an > approximation of a second based on earth orientation. Pick an epoch in the > 1950's and call it TAI and we have something with a 60 year track record, > which is more than you can say for the current UTC :) > > Too bad the ITU thing doesn't include the 36 second delta for safety... > > Warner _______________________________________________ LEAPSECS mailing list [email protected] http://six.pairlist.net/mailman/listinfo/leapsecs
