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Bill, you wrote:
"If you ARE attempting this at home without a tripod  mount or clamp, by all
means run--don't walk--to your nearest hobby/crafts  shop and pick up a
package of Plasticine (a non-drying modeling clay) to  pound on the surface
and push your sextant legs into. It comes in small,  cheap quantities--the
last I checked.  A couple of marble-sized chunks  of beeswax could work as
well."

Yep. I first used some little bits of  clay from the toy section of the local
Walgreens. I've also had very good  results with an old mousepad. Any sheet
of rubbery material with a rough surface  on both sides should work.

A good way to verify that there has been no slippage is to re-measure the
very first angle every now and then. It should be the same within +/- 0.1
arcminutes.

Another experiment to try:
Find a laser pointer, preferably one with that you can leave on for a  while,
like a laser level from a hardware store (<$15). Set the sextant on  its side
on a table in a long hallway and set it for 0deg 0.0 minutes. Aim the  laser
through the telescope shifting it up and down until you see two spots of
light on the far wall. Adjust the focus of the telescope until those spots are
razor sharp. You should be able to get them down to 1mm in size. Are they on the
 same level in a line that is parallel to the sextant frame? No? Then you
sextant mirrors are not parallel to each other (there are two possible
adjustments here). Are the spots the same distance apart at different distances  from
the sextant? No? Then you've got an index error. If you can do this test at
distances of, say, 25 feet and 125 feet, you should be able to adjust your
sextant's index correction accurately and repeatably to an accuracy of <0.1
minutes of arc.

I've tried this with several different sextants. It seems to work great.  The
lowest magnification telescope will probably work best. You'll want one that
can focus close. The ability to focus the telescope is important since most
lasers diverge significantly after a few dozen feet.

-FER
42.0N 87.7W,  or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars

   

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