On Mon, 09 Feb 2004, Edward Smith <emarksmi@san.rr.com> wrote:
From what I could gather, what you are doing is using the error in the
tracking to correct your polar alignment. The manual actually has all
of the directions (up, down, left, and right) and how to correct.
I'll have to play with the geometry until I understand it.
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There's one sure way to align your scope with the cardinal
directions. The freeware Swiss Ephemeris/JPL-DE406 casting
a shadow at noon LAT on a LEVEL flat surface will draw the
north-south line--literally--such that you can know what's
exactly true north. You need a very flat planar surface as
level as a quality pool table. You'll need a plumbbob such
that it is mounted several feet above the flat surface and
generally stationary with less than a calm breeze. And you
need to know the exact geographical longitude and latitude
of the plumbbob, at least down to the nearest second, give
or take. This is imperfect due to variances in gravitation
in specific locations, but you'll be able to strike a line
pointing very nearly true N-S, closer than any other crude
method. A quality GPS is preferable, although you can come
close enough with the USGS terraserver website, etc. There
are better methods using stars, but they require extensive
calibration. By this method, you can do it in five minutes
or less--and in broad daylight, and achieve great accuracy.
Just enter your location in Astrolog w/SWEPH, available at:
http://www.bdcol.ee/astrolog/changed/a541gwin.zip, and get
the JPL ephemeris at ftp://ftp.astro.ch/pub/swisseph/ephe/.
Just set houses at "meridian", and calculate solar transit
for the day you'll be striking your N-S line by the shadow
cast from the string of your plumbbob at 12:00:00 Noon LAT.
Enjoy!
Daniel Joseph Min
*DOWNLOAD FREE Precision US Map Coordinates:
http://terraserver.microsoft.com/default.aspx
*DOWNLOAD FREEWARE Shadows Sundial Program:
http://web.fc-net.fr/frb/sundials/gb/defaut.htm
*DOWNLOAD FREEWARE Carte du Ciel:
http://www.stargazing.net/astropc/index.html
*DOWNLOAD FULL-FUNCTION DEMO of SkyMap:
http://www.skymap.com/smp_eval.htm
ftp://ftp.ttp.co.uk/smp9eval.exe
*Min's Newsgroup-Archived Home Page On The World Wide Web:
http://groups.google.com/groups?selm=5YTK57VH37948.6355092593@Gilgamesh-frog.org
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