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Here is another use of celestial techniques that you probably didn't
know about.

When firing long range cannons at targets many miles away that are
not
in sight you must calculate in exactly what direction you must point
the
guns to hit the target and at what elevation you have to launch the
projectile for it to travel the exact distance to the target. You
take
into account many factors including powder temperature (warmer powder
burns faster creating more pressure, raising muzzle velocity), bore
erosion (each shot causes some of the bore to wear away allowing more
powder gasses to escape around the projectile resulting in lower
muzzle
velocity),  the exact weight of the projectile, winds and air density
at
different altitude levels (some projectiles go up to 30,000 feet in
altitude), the difference between the height of the guns and of the
target above sea level, the fact that the trajectory is not rigid in
space, that gyroscopic and aerodynamic forces working on the
projectile
cause it to drift to the right (with right hand rifling), and that
the
earth will turn an appreciable amount while the projectile is in
flight
which can be up to ninety seconds. It goes without saying that you
must
accurately know the location of the guns and the target for the
computation.

It is also necessary to determine a very accurate direction reference
for the sighting equipment on the guns. The person in charge of
positioning the guns uses an "aiming circle" which is an instrument
much
like a transit to do this. But first he must establish direction for
the
aiming circle and there are several ways to do this. The least
accurate
way is to use the built in compass but this is only accurate to about
ten mils, about one half of a degree. A better way is for a survey
team
to come to the position which establishes the coordinates of the
position and also a direction by the positioning of two stakes on a
known azimuth as established by the survey party. This is good to one
mil.

There are also two methods which utilize celestial. One is called
"simultaneous observation" in which personnel at battalion
headquarters,
at a prearranged time,  track the sun with an aiming circle while the
three outlying firing batteries at three different locations (10 to
15
kilometers away) do the same while listening to battalion on the
radio
saying "tracking...tracking...tracking...tip" at which point you stop
tracking the sun and deflect the line of sight down to ground level
and
direct an assistant to emplace a stake on that azimuth. The
headquarters
then informs you what that azimuth is that they have determined, most
commonly by survey, or by celestial computation.

Another method of establishing direction involving celestial involves
using the aiming circle to observe polaris. You set up the aiming
circle
and set the recording scale to zero. You then sight on polaris using
the
non recording motion to move the line of sight right or left which
allows the scale to remain set on zero. After you do this you use the
recording motion to measure the azimuth of kochab in relationship to
the
zero point established with polaris. You then looked at a graph
contained in Field Manual FM 6-50 which gave you the true azimuth of
polaris based on the azimuth of kochab (actually the difference in
the
azimuth of polaris and kochab.) This allowed for the daily movement
of
polaris around the true pole. You then returned the aiming circle
telescope to the zero point, deflected it downward, and had an
assistant
emplace a stake on that azimuth. The graph in FM 6-50 was calculated
for
the latitude of Germany (go figure) and for the 1970s. I don't
remember
the graph being updated to allow for the change in the coordinates of
polaris.


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