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Subject: Re: [M]: LX200 tracking frustration
From: Bill Arnett
Reply To: mapug@shore.net
Date: Fri Oct 18 02:06:16 1996

At 8:33 PM -0700 10/17/96, R. Aguirre wrote:
>Bill Arnett wrote:
>>... It is better to choose stars that are approximately between 30 and 60
>> degrees elevation. Too close to the horizon introduces Dec errors due to
>> atmospheric refraction (which is NOT corrected for in the alignment
>> process); too close to the zenith introduces RA errors due to the geometry.
> Thats not exactly true Bill, one of the features of software version
>3.34 is that if the exact latitude and longitiude is stored in one of the
>4 site locations ( I use a GPS to give me the coordinates) in the
>database, the LX-200 compentates for atmospheric refraction. Thats the
>"only" reason latatude and longitude need to be entered, so the scope
>knows to compensate for that refraction..... and it works!

My understanding is that the refraction correction is not applied DURING
the alignment process. Of course, I'm only repeating what I've heard here.

> The explaination is in the owners manual.

But not on this point :-(

Of course, it should be noted that the refraction correction is quite small
unless you are very near the horizon (and probably very bad seeing). At 10
degrees elevation the refraction is about 6 arcminutes, probably less than
the LX200's mechanical accuracy.

---
Bill Arnett              billa@znet.com           http://www.seds.org/billa/

  "I know that I am mortal and the creature of a day; but when I search
   out the massed wheeling circles of the stars, my feet no longer touch
   the earth, but, side by side with Zeus himself, I take my fill of
   ambrosia, the food of the gods." -- Claudius Ptolemaeus (Ptolemy)