Re: ATM Global Positioning System

["Jack Brindle" <jackb@ricochet.net>]

>Perhaps Meade should incorporate an  Oncore board in its LX series of
Go-To
>scope.
>Then when turned on, the scope would know the precise time and exactly
where it
>was located. I'm surprised that neither Mel nor Chuck have incorporated
this
>feature in their computer-controlled scopes :-).
>

I have taken a close look at this for the MacDobs system, and have plans
for a GPS module. In fact I have had quite a bit of discussion with several
amateur astronomers, both in this forum and those in the San Jose area.

Let's see if I can reconstruct the gist of these discussions. Bear with me,
this is a bit fuzzy. Hopefully those more knowledgable than I can explain
it better.

Three entities are needed to establish absolute position and time for any
given site. These are the geographical location (lat, long) on the earth,
the current sidereal time, and the location of at least two guide stars.
Since there are actually four or five points of reference given in the
above set, and we only need three points, an absolute position can be
established quite nicely. A GPS can give you two of the three references,
with star alignment giving the third. Or, using star alignment and the
current longitude or time, the remainder can be calculated. Three star
sightings define an absolute position in space. You then need an additional
quantity to establish the position on the earth. Since we don't need to be
all that precise in our calculations (especially with the wide tolerances
we use in our scopes and measuring apparatus), we can just about guess the
thrid quantity and correct for it with our measurements. So, "watch" time,
or the general latitude and longitude are "good enough" to get us to where
we need to be. After that, we get closer and closer to precision with every
additional star alignment we make.

So, having GPS then becomes an "it might be nice for those needing more
toys" or a holiday gift or something like that. Now, because I happen to
have a GPS receiver, I will probably create a GPS module for the MacDobs
system to do this. That is, assuming I can get working on the module before
my GPS receiver becomes useless next September. The more important piece of
this puzzle is to have the ability to accurately align a scope to stars,
and the ability to use that information in the star calculations.

So, Mel (and others) how was my explanation?

-JackB
===================================================================
"My name is bud lightbeer. I come in pieces!"