[SJAAboard] FW: First Impressions: Scope 9 C-11 f/10 Compustar

[Rob Hawley (SJAA)]

They built a Y2K problem into the User Interface - unbelievable!!!

At the moment the tracking gears are not engaging. I will keep this in mind
and will have to document the workaround on the web page.


Rob Hawley 

>-----Original Message-----
>From: Jim Van Nuland [mailto:jvn at svpal.org]
>Sent: Friday, January 11, 2008 6:22 PM
>To: Business list for SJAA board of directors
>Subject: Re: [SJAAboard] FW: First Impressions: Scope 9 C-11 f/10 Compustar
>
>   There is another consideration with that scope's electronics.
>
>   The first two digits of the date are fixed at 19, so you can't
>directly enter (say) 2008.  The trick is to subtract 4 from the
>real year until the result is less than 2000.  For the present
>year, enter 1996.  The resulting error is about 7 seconds of RA
>error per 4 years.  So in 2008, the error is 5.5 arc-minutes of
>pointing error, or 1/5 of the moon's diameter, in a consistent
>direction.
>
>   The error is due to the calculation of local sidereal time
>starting from the date and time.  When the year is off by 1, the
>error is about 3 minutes of time, or 0.75 degrees.  But after 4
>years, the "leap" nearly cancels the accumulated error.  That's
>why the adjustment must be done in 4-year steps.
>
>   One could enter a slightly incorrect time to eliminate the
>error.  As to the amount and sign of the adjustment, I leave that
>as an exercise for the reader, or as an experiment for the observer.
>
>   Paul Barton pointed out restriction to me about 10 years ago,
>and we experimented by setting the year 4 less than real.  It
>worked fine for finding objects.  By now a small guiding
>adjustment would be needed.
>
>Clear Skies!
>--
>Jim Van Nuland, San Jose (California) Astronomical Association
><a href="http://www.svpal.org/~jvn/ ">JVN's web site</a>
>
>
>
>
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