So, let’s consider another possibility, and calculate from perihelion to perihelion.  According to the US Naval Observatory, the last perihelion was at 3pm UTC on January 3, 2010, and the next will be at midnight on January 3, 2011.  Turning again to Frink, that would give us a date of April 29, 2010 at around 3pm UTC.

#2010-01-03 15:00 UTC#+((#2011-01-03 00:00 UTC#-#2010-01-03 15:00 UTC#)/pi)->UTC

Any further refinements are appreciated!

The above calculation is based on a naïve assumption of the Earth’s velocity as a constant.  Since Kepler’s Second Law tells us that the orbital velocity of a planet is faster when it is closer to the sun, the date suggested above is undoubtedly imperfect.

Frink is a fantastic tool for performing all manner of interesting calculations and conversions.  You might find this Frink formula useful as a starting point for exploration:

#2009-12-21 17:47 UTC#+((#2010-12-21 23:38 UTC#-#2009-12-21 17:47 UTC#)/pi)->UTC

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