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I How to find the position of a celestial object in the sky?

  1. Jan 13, 2019 #1
    Hi all,

    I am an electrical engineering student currently involved in a project aimed to create a simple GoTo azimuth mount. I don't have a lot of background in astronomy, so I am a bit confused on how to find the position of a star in the sky.

    After some research on my own, I figured out that the following information is necessary (maybe not enough):

    1. My location on earth

    2. Time in my current time zone

    3. The right ascension and declination of the star I would like to find

    I was then confused by a flood of astronomy vocabularies. In order to understand the process better, I really need a concrete example.

    So for example,

    I am located at 40.4259° N, 86.9081° W, and I wish to find Andromeda galaxy (RA = 00h 42m 44.3s, Declination = +41° 16′ 9″, I found this data on Wikipedia) on the sky at 1:00 AM EST January 13th, 2019. Assume we have the telescope calibrated and pointed at the north pole star (I am not sure if this is enough as a reference point), how would I move the telescope to find the Andromeda galaxy then?

    This might be a terrible example, I am just writing down some random numbers and time hoping it might work. If you think this example is wrong, please please provide a similar example! I really need to work through some examples to be able to understand all these! Thanks a lot in advance!!
  2. jcsd
  3. Jan 13, 2019 #2


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    Hi Xinran :welcome:

    Not an astronomist myself either. But the
    appears to be all clickable. So either ask a specific question when you get stuck at some particular point, or grab a textbook and study the base material. PF is not intended as a resource for the latter but as a place to ask questions about stumbling items in there.
  4. Jan 13, 2019 #3


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    This calculator may be of use. Given the RA and Dec of the object, your latitude and longitude, and your local time, it will calculate the altitude and azimuth of the object. For the example you gave, the Andromeda galaxy has an altitude of about 63 degrees and an azimuth of about 76 degrees. So it is 14 degrees north of due east, and 63 degrees above the horizon. Normally for an object like the Andromeda galaxy, you would find it with your naked eye or a pair of binoculars and aim the telescope at it manually. To point the telescope using GoTo mount is more complicated and depends on the details of the mount and the telescope.

    Edit: If you're trying to create a GoTo alt-azimuth mount, then you need two things. You need the mount to be level, as this sets the plane of the horizon and hence the altitude. Second, you need to find true north to set the zero point of azimuth. Once you have those two things, you calculate the altitude and azimuth of the object using the calculator I linked, and go to those values. Note that the site I linked has the necessary formulae below the calculator itself.
    Last edited: Jan 13, 2019
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