Bruno Wolff III <bruno@wolff.to> writes:
> Wikipedia gives 365.242189670 days (86400 seconds) as the length of
> the mean solar year in 2000. To give you some idea of how constant
> that values is, Wikipedia claims that 2000 years ago the mean solar
> year was about 10 seconds longer. Using the above value I get there
> is an average of 2629743 seconds in a month.
> And yet another option is to note that in the Gregorian calendar there are
> 400*365+97 days or 400*12 months in 400 years, which gives 2629746 seconds
> per month on average.
I like the latter approach, mainly because it gives a defensible
rationale for using a particular exact value. With the solar-year
approach there's no strong reason why you should use 2000 (or any other
particular year) as the reference; and any value you did use would be
subject to both roundoff and observational error. With the Gregorian
calendar as reference, 2629746 seconds is the *exact* answer, and it's
correct because the Pope says so ;-).
(Or, for the Protestants among us, it's correct because the SQL standard
specifies use of the Gregorian calendar.)
regards, tom lane