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Thread: Does a GPS unit allow a telescope with a computerized goto mount to track to any star

  1. #1

    Question Does a GPS unit allow a telescope with a computerized goto mount to track to any star

    without a manual three star, two star or solar system alignment using the hand control?

  2. #2
    Join Date
    May 2005
    Quote Originally Posted by nitelitegirl View Post
    without a manual three star, two star or solar system alignment using the hand control?
    It's accuracy might not be adequate.

    There is a free iPhone app that allows you to point your phone in any direction, and it will tell you what star/planet/etc is in that direction.

  3. #3
    the one I'm thinking about is this one - Is this designed to interact with the telescopes' associated computer to point the scope in the correct location? It says 16 channel but I'm not sure if that's very precise or not. I heard civilian GPS is not as accurate as military versions.

  4. #4
    Join Date
    Dec 2006
    Equatorially mounted a scope can track a star without any need for GPS or star alignment. It can't find the star for you without it however. So I'll assume you are talking about an alt azimuth mounted scope.

    The point of a three star alignment is to determine several things. Location on the earth (nearest mile is sufficient), date and time, orientation of the mount both as to north and as to how level it is and how accurately the optical axis of the telescope is aligned with the mechanical axes of the mount. It is never perfect. A GPS can find some but not all of the needed information. For those it can't provide the three star system can. Don't worry about the accuracy of the GPS it will be way more accurate than the scope's gears and mount are and a non issue. If your scope were perfect mechanically and set up absolutely level (to surveyor accuracy) then you might get away without doing star alignments. Since that won't happen you'll still need them.

    I'm not convinced a GPS speeds things up all that much. It can take a unit 15 minutes to acquire enough satellites and collect enough data for it to know the date, time, and location to an accuracy an experienced observer would already have entered via an accurate 3 star alignment. Still it does catch errors caused by aligning on a star different than you tell the scope it is pointed at.

    The only system I've seen that can do all this automatically is the new Meade LS series with built in CCD as well as GPS. Still it isn't perfect as it gets confused sometimes if the star it wants to use is behind a tree or cloud. It can take 15 to 30 minutes to find itself and be ready to use. I'd have it long done manually by then.


  5. #5
    Join Date
    Sep 2006
    i think the answer is just means you dont have to manually input time and location. these days we have that info at our figertips even if you travelling to different sites.
    as Rick said, gps can take a lot longer to get a fix than just inputing the data yourself anyways..mine certainly does
    there is usually a sync function somewhere if you are concentrating on one particular target...that works well i find, but only worth using it if you staying on that one target...its tends to muck up subsequent gotos otherwise.
    Last edited by mutleyeng; 2012-Apr-08 at 08:03 PM.

  6. #6
    Join Date
    Jul 2003
    SW of the town of Maricopa, AZ. This is in the southern Arizona desert.
    Quote Originally Posted by nitelitegirl View Post
    without a manual three star, two star or solar system alignment using the hand control?
    Having used a telescope with integrated GPS, I can say that the answer is no.
    To qualify:
    My scope was permanently polar mounted and aligned. Thus, I did not need to do any of the alignments you asked about. What the GPS allowed for was warning me whether the object that I wanted to goto was indeed above the horizon at that time.

    If your scope is not permanently polar mounted, then you would have to do your alignment routine every time that you set the scope up.

    What the GPS would do, in that case, is make it easier by not requiring you to manually input your location and time.
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  7. #7
    Join Date
    Sep 2006
    hey nitelite,
    just read your other thread where you say what scope you have.
    so long as you can input the day, time within a few minutes, and location to the nearest city (say 30 miles is fine, might be more) then thats good enough. All you really are doing is giving the scope a heads up as to where it suggests the alignment stars are, or lets it make a good guess at what ones you are pointing at.
    i dont know if you are using an auto align, or choosing you own alignment objects.
    Just dont use the moon as an alignment object if you are trying to view deep sky. Also, if you have mostly been viewing the planets, when starting to view deep sky use low power eye pieces. Ive nver used a mak 127, but i think its quite a narrow field of view...for deep sky you really want wide field, so if you dont already have one, a 32mm eye peice would be money better spent than the gps.

  8. #8
    well, I just recently started trying to use three star alignment but although the computer says it was successful when I try to tell it to move to another star it does not seem to find it properly. For reference, I used the Orion constellation and aligned to Betelegeuse, Bellatrix and Rigel.

  9. #9
    Join Date
    Sep 2006
    ok, i think thats the reason for your inaccuracy, they are all in the same region.
    keeping it simple, the wider the spread of star you use the, one north, one west and one east.
    there are specific criteria you can use for which stars give best results, but for now just dont pick them in the same constellation and it should be much better results.
    to be honest, i just do 2 star east and one west, and that is good enough to find any messier target, but you do need to be using a low power eyepiece. if i had a 9mm EP in it would miss the target every time.

  10. #10
    Join Date
    Jan 2008
    It's also important that the stars are separated "sufficiently" in both declination and right ascension. Which stars or where in the sky to choose tham depends on your latitude and the date/time.

  11. #11
    Join Date
    Oct 2011
    Fresno, CA
    I have a Celestron CPC-800, which has a built-in GPS and full computer control for GoTo and tracking. Within our local club, there is a variety of both GPS and non-GPS computer controlled telescopes, not to mention all manner of "push-to" scopes.

    The purpose of the GPS unit is simply to tell the telescope's computer the location (Lat/Long) of the telescope and the date and time. That's all. However, this data is crucial (along with the alignment objects) for modeling the sky so that the telescope can accurately find and track objects. With a non-GPS telescope, it is necessary to enter the location, the date, and the time. After that, the GPS and non-GPS scopes behave about the same. I can turn off the GPS feature on my scope so that it behaves just like a non-GPS scope.

    With regards to linking with the GPS satellites, my scope generally takes about a minute unless it has been moved a long distance. We did a 350 mile trip for the annular solar eclipse and satellite linking took about 2 minutes. The CPC manual says that initial power-up with a new scope can take 3 to 5 minutes, which I recall as being accurate, and up to an hour for a very long distance move, though I've never had that happen. I think the time lag after a long move is because the computer remembers the previous location and where the satellites should be. I suspect the computer starts out "confused" if the satellites are not anywhere near where it expects them.

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