On 1/8/2015 12:13 PM, Justan Olphart wrote:
On 1/8/2015 11:05 AM, 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?v=eeQwYrfmvoQ

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?v=eeQwYrfmvoQ

".. 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.


You haven't mastered left, right, up, and down yet. You aren't ready for
a sextant yet.


In the cub scouts we learned to use a ruler held at arms length and a
bit of math to get the height of a tree or anything really.