Telescope Reviews: Re: Degree Circles

Observing conditions weren't looking very good today, but I had some fun putting together a little web-based utility for calculating positions on setting circles on a Dobsonian from ra/dec using two star calibration (no need for polar alignment or leveling). This uses the Taki formulae which only work if you have two setting circles (it'll work with azimuth circle plus inclinometer, but only if your azimuth circle is leveled; otherwise, it'll be off a little).

Anyway, the link is:
http://pruss.homeip.net/alex/cgi-bin/radec.pl

The idea is this. You need internet access while observing. (On a cell phone, or a laptop, or a PDA. The site is no-frills, text only, and should show up on any rudimentary browser that supports forms.) You also need a list of ra/dec for some bright stars (I could build that in eventually).

You choose a bright star, and enter the ra/dec (in decimal, not DMS, format, i.e., hours.ddd or degrees.ddd) into the form under "Reference object 1". Then you point the scope to the star, and enter the azimuth and altitude that your setting circles show into the blanks. You click on "Set first reference object". You repeat with a second star, hopefully in a completely different part of the sky, or else your precision will be low, under "Reference object 2".

Then, you put the RA and Dec of the object you want to observe under "Object to locate", or you put in a Messier, Caldwell or NGC catalog number (e.g., ngc1244 or "M13" or
"c 48"), and choose "Calculate". You will then get the alt and az for that object at that moment.

There are probably a bunch of bugs still there.

Another, simpler, web-based utility does the same thing, but using real alt/az coordinates instead of ra/dec coordinates, and aligns the real alt/az coordinates with the scope's alt/az coordinates. That requires a source of alt/az coordinates (e.g., a PDA with astronomy software, a laptop, etc.).

http://pruss.homeip.net/alex/cgi-bin/taki.pl

Both of these are running on one of the computers at home, so please don't abuse them.

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Coulter Odyssey 13.1" split-tube
Coulter Odyssey 8"
Home-made 7.8" F/4 dobsonian travel scope
Home-made 68mm F/5.3 achro (typically used as finder on 13.1")
Skymaster 15x70
BPTs4 8x30
32mm Plossl, 30mm Rini, 27mm Kellner, 13mm Hyperion, 6mm TMB/BO Planetary, Owl 2X Barlow
Palm TX with AstroInfo and RescoViewer

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