Gerald Kelleher wrote:
On Monday, January 5, 2015 6:09:51 AM UTC-8, Tim wrote:
This is great reading especially for the technically challenged like me.
With my style of lake boating its more like " hey, let's go that away!"

Keep it coming though. This is all good to know...

Although the Egyptians knew nothing of daily rotation and the orbital
motion of the Earth around the Sun, they realized that they could not
base their year on a constant stream of 365 days. The flooding of Nile on
which their culture depended coincided closely with the annual appearance
of Sirius one morning hence their awareness of the brightest star in the
celestial arena for practical reasons and the fact that it skips an
appearance by one day after 4 years. In dynamical terms, the additional
24 hours represents the orbital distance the Earth needs to travel to
bring Sirius back into view or what now has become the February 29th
rotation. We omit 6 hours of orbital motion each non leap year as we
gauge our day solely by daily rotation and this accumulates to roughly 24
hours of missing orbital distance at the end of 4 orbital circuits and 4 years.

It isn't really possible to continue with the narrative without an
explanation which contains the leap day rotation and what it represents
in dynamical terms. Perhaps another could explain it better and I have no
objections to this however the facts will remain roughly the same.

The maritime tradition, much like astronomy, is among the most noble and
ancient human endeavors in terms of sophistication so that people
generally don't think of their ancestors in terms of primitive but rather
look for the roots of contemporary traditions in older methods and
insights. The rules governing navigation from boats to aircraft are one
thing but the timekeeping systems on which navigation is based in
something else and this requires some knowledge of the Earth's daily and orbital cycles.

The Egyptians may have known of the rotation and even of the orbit. Forget
which Egyptians calculated the diameter of the earth. They were only off
by about 225 miles, using sticks and shadows at a certain time. Way before
Europe and Rome admitted the earth was not flat.