On Monday, January 5, 2015 7:48:22 AM UTC-8, Tim wrote:
Gerald, it's all amazing isn't it?

http://www.gautschy.ch/~rita/archast...liacsirius.JPG

To recap, when the Egyptians saw Sirius appear one morning after an absence behind the glare of the Sun for a few months they knew it would appear again 365 days later, yet again after another 365 days and then again on the third cycle of 365 days but on the fourth 365 day cycle Sirius was nowhere to be seen. It would appear the next day hence the extra rotation that we know as February 29th.

Each non leap year the Earth falls behind in position by 6 hours of orbital motion which accumulates to 12 hours after the second 365 day day cycle,18 hours after the third cycle and a full 24 hours on February 28th of a leap year. The extra rotation corresponds to 24 hours of orbital distance the Earth travels so that it completes 4 full orbital circuits using 1461 rotations as a gauge. This in turn reduces to 3651/4 rotations per circuit.

The next step is a fairly intricate one as the 24 hour day makes an appearance within this framework of 365/366 days.