Re: GPS on a German Equatorial Mount

Joe Zeglinski

Hi Marj,

Just one question about "time precision". I think the GPS unit might give
you the EXACT time at your precise location - give or take 10 metres I
believe, for the non-military GPS. If so, the GPS time won't be in agreement
with your usual "Time Zone" which is one hour wide. If your observing site is
right in the middle of a time zone, then they agree, but if you set up +/- 30,
minutes away from the centre of the zone, doesn't the GPS give you that exact
time, rather than the time zone standard time? So, while the UT is always
correct, the rest of the world is on a one hour wide approximation of actual
time. There are only 2 correct time references - GPS time, and the Right
Ascension of the star overhead - both are accurate for the site geographic

In the olden days, B.C. (before high speed electronic confusers), we
would calculate time for the geographic spot, with a lot more care, perhaps.
It would be interesting to compare the time displayed by a GPS unit and the
observer's local time. Then again, the GPS works only in UT, so site
coordinates are irrelevant, for this.

Consider this. An AP mount owner goes out and has to enter the GMT into
the controller. Not having a GPS unit, he looks at his wrist watch, adds or
subtracts his Time Zone correction, and declares this to be the exact UT.
However, he may be +/- 30 minutes away from the centre of the zone, so the
setup is way out.

The question here is whether we are supposed to add the time zone Latitude
delta ourselves, or does the AP's GTOCP3 controller look at the observer's
site coordinates and compensates for the "site's longitude difference" for us?
I don't think this is stated anywhere in the manual. I suspect that the GTOCP3
does not compensate, so the GPS based UT would be exact, even 30 minutes
different from the standard non-GPS based mount setup.

Marj, at the very least, the AP firmware should make the corrections for
the user entered time zone based, UT. It's such a hassle to pencil in the
local time zone delta, to the wrist watch based time. That's where the GPS
would be valuable.

But ... I don't know if all that exactitude really matters, in most cases.


----- Original Message -----
From: "Marj" <>
To: <>
Sent: Friday, June 15, 2007 7:12 PM
Subject: RE: [ap-gto] Re: GPS on a German Equatorial Mount

Dear Paul,

I agree, but the GPS question keeps coming up in this group every other
month or so........

Marj Christen
Astro-Physics, Inc
11250 Forest Hills Road
Machesney Park, IL 61115
Phone: 815-282-1513
Fax: 815-282-9847
Please include this e-mail with your response.

-----Original Message-----
From: []On Behalf Of
Paul Sterngold
Sent: Friday, June 15, 2007 10:16 AM
Subject: Re: [ap-gto] Re: GPS on a German Equatorial Mount

As I see it, the key benefit for GPS is obtaining accurate location and time
info when setting up in the field. But this can be done with a handheld
unit, which offers more versatility than a dedicated unit attached to my
mount. The only benefit to the dedicated unit is that it directly uploads
this info to the mount, as opposed to the few seconds it takes me to act as
the interface device and manually enter the information into the mount's
handbox. All things considered, I do not believe that GPS is a significant
selling point for an AP mount. Your mounts are typically used by more
knowledgeable astronomers and astroimagers, versus, for instance, Meade and
Celestron mounts that are often used by newbies. For them, simplicity and
turnkey operation is probably more important. Just my $0.02 worth.

As others have suggested, there are other areas to invest R&D dollars that
offer true benefits to your users. I think the ideas already suggested- USB
and Bluetooth- would be excellent new features.

Paul Sterngold

ayiomamitis < ayiomami@otenet. <> gr> wrote:
--- In ap-gto@yahoogroups. <> com,
"nfoldager" <nf@...> wrote:

I don't care about GPS on the mount. However, Rolando, listening to
ones wife ...
Me too. GPS is not an issue for me ... but an added expense and one
more thing to go wroung.

Best regards,

Niels Foldager

P.S. I do, however, use a handheld GPS as an acurate clock input for my
laptop when tracking satellites.
Exactly. If I need GPS, I can pick up a unit from eBay brand new and
quite cheap.


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