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Califbill

True North wrote:
On Saturday, 3 January 2015 13:36:04 UTC-4, wrote:
On Sat, 3 Jan 2015 08:14:26 -0800 (PST),
wrote:

This is the broadest possible overview for those who are unfamiliar
with how the motions of the Earth fit in with human timekeeping and
although it is an injustice to those people who created the system we
use today, the overview is much better than none at all. There is no
stopping to differentiate between the original geocentric astronomers
and their observations from the later heliocentric astronomers who
worked off the idea that the Earth moves between Venus and Mars around
the Sun so readers today don't concern themselves with the level of
knowledge of any given era as this will be taken for granted in order
to move the story along.

As the Earth moves through space in its circuit around the Sun,certain
stars lying on or near the same plane as the Earth's orbital motion are
temporarily lost behind the Sun's glare. The older astronomers marked
the passage as the Sun through the constellations (hence birth signs)
but for purposes of this story it is better to consider the apparent
motion of the stars behind the Sun due to the orbital motion of the Earth -

https://www.youtube.com/watch?vîQwYrfmvoQ

The anchor for the Lat/Long system originally was based on the
appearance of one particular star as the orbital motion of the Earth
placed the star just far enough to one side of the Sun one morning,
That star was the brightest one in the celestial arena known as Sirius
and can be seen on the bottom left of the image -

https://www.youtube.com/watch?vîQwYrfmvoQ

".. on account of the procession of the rising of Sirius by one day in
the course of 4 years,.. therefore it shall be, that the year of 360
days and the 5 days added to their end, so one day shall be from this
day after every 4 years added to the 5 epagomenae before the new year"
Canopus Decree 238 BC

Unbeknownst to themselves, what the Egyptians were actually doing was
defining the Earth's orbital position around the Sun using the seasonal
appearance of a star as a gauge and the number of rotations that fit
inside an orbital circuit, in this case 1461 rotations for 4 orbital
circuits which breaks down into 365 1/4 rotations to one orbital circuit.

This is the founding principle where one 24 hour day keeps in step with
one rotation of the Earth and the basis of the Lat/Long system along
with the reason why the extra day and rotation is introduced in order
to keep the Earth's position in space fixed by the number of
rotations,at least to the nearest rotation.

The next step is the process which equates the 'average' 24 hour day
with 'constant' rotation insofar as the average 24 hour day substitutes
for constant rotation through 360 degrees in that period.

I am reacquainting myself with celestial mechanics as I am playing
with my new sextant.

I've thought about buying the Davis 25 plastic sextant to play with. one
practical use would be to confirm the height of the huge Linden trees
that border my back yard.
I did a google search and found a link that described how you could
estimate height with an upside down protractor, a string with a weighted
object as a kind of plumb bob and a ruler to sight along.The ruler would
sit on the upside down base of the protractor and the string would give
you the sighted angle. The guy provided the formula to get a fairly accurate height.

Basic geometry.