Calculating Older Time

[cardinalrules]

I would like to know the exact time in 2005 that corresponds to Sept 5 2004, at 2am.

[admin]

How do you mean -the time in 2005 when the Earth is in the exact same point in its orbit as it was at Sept 5 2004, at 2am (I'll assume GMT) If so, the mean value for a tropical year (from one vernal equinox to another) is 365.242189670 days. I got this value from Wikipedia. It does change slightly over time, due to changes in the earth's orbit.

Also, the value changes in reference to different positions in the earth's orbit. The Wiki value for the autumnal equinox (which Sept 5 is close to) is 365.24201767 days.

The Julian day for 2:00:00 GMT on Sept 5, 2004 is: 2453253.58333 Adding on the value of a tropical year (autumnal value), which puts the earth at its same point in its orbit a year later yields: 2453618.82535 Which is 7:48:30 GMT on Sept 5, 2005.

There are other definitions of a year, though. Is this what you are looking for