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    Re: Celestial navigation in the field artillery
    From: Gary LaPook
    Date: 2007 Aug 18, 22:48 -0700

    I found a link to FM 6-50 chapter 5 which contains the information
    about these techniques.
    On Aug 17, 2:41 am, glap...@PACBELL.NET wrote:
    > 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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