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Subject: Re: [M]: LX200 clock accuracy
From: Bill Arnett
Reply To: mapug@shore.net
Date: Sun Jan 18 02:23:50 1998

At 2:41 PM -0800 1/17/98, James W. Burrows wrote:
>At 19:43 98-01-16 -0700, Chris Vedeler wrote:
>
>>Try it and see for yourself. Get your scope well aligned and with
>accurate time. Goto star 905 and see how close Jupiter gets to the center
>of the field. Then reset the time 20 minutes fast. Then Goto star 905
>again and see how much it moves. The scope will not slew 5 degrees (how
>much the stars move in 20 minutes) it will slew a few arc seconds (if that)
>to where Jupiter would be against the background stars 20 minutes from now.
>>
>
>I don't think (but I don't know) that the LX200 software works that way.
>Suppose that it just calculates the RA & DEC of the planets when you power
>up the scope, looking only at the date. Then the clock could be off by
>hours and it wouldn't make any difference. My reason for guessing this is
>that the keypad says "Recalulating planetary coordinates" after you change
>the date, but not the time...

Chris's experiment might be rescued by changing the date in addition to the
time thus forcing the LX200 to recompute the planetary positions. Saturn,
eg, doesn't move very far in a day (about 4 arc minutes right now). If you
set the date 25 hours ahead it will compute Saturn's position to be 4
minutes off from where it really is but will NOT think that the sky has
rotated the extra hour.

---
Bill Arnett "Science is a way of trying
San Jose, CA USA not to fool yourself." -- Feynman
billa@zNet.com <URL:http://www.seds.org/billa/>