[LEAPSECS] Straw men

[Rob Seaman]

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
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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