It's amazing that someone was able to calculate these
numbers out to 6 decimals. Is that done by some type of
observation or is it mathematics?

How could you possibly measure something like that?



On 3/25/2011 1:14 PM, Kevin Karney wrote:
Nothing is constant in the heavens !
The 'tropical' year (from equinox to equinox) is 365.242190 days
The 'sidereal' year (fixed star to fixed star) is 365.256363 days
The 'anomalistic' year (perihelion to perihelion) is 365.259636 days - cycling 
over a period of some 21000 years
(values for 2009 from Astronomical Almanac)
But these are mean values having averaged out the effects of nutation (the 
wobbling of the Earth's axis) and various other effects.

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