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Thread: RA and DEC coordinates?

  1. #1
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    Default RA and DEC coordinates?



    Hi all.

    Really sorry if this is a silly question however I've learnt how to polar align now yet im struggling with a stars coordinates over an evenings viewing.

    For example, take Mizar. Using the setting circles on an EQ2 mount (I know their not too accurate but using them as an example), the coordinates at say 10pm will be X and Y.

    By 1am for example are they the same or will they have changed? If they have changed, where do I find out the new X and Y?

    I've been looking on YouTube etc all afternoon and this really escapes me.

    Again, apologies if this sounds daft.

    Thanks in advance.

    Carl

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    Default Re: RA and DEC coordinates?

    download a free app called stellarium , it will show you updates on thousands of targets, planets,deep sky,satellites, it will give you alt az and eq positions in the sky which you can translate to your mount/ setting circles
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    Default Re: RA and DEC coordinates?

    Quote Originally Posted by yobbo89 View Post
    download a free app called stellarium , it will show you updates on thousands of targets, planets,deep sky,satellites, it will give you alt az and eq positions in the sky which you can translate to your mount/ setting circles
    I am literally installing Stellarium now! I'm presuming this software will give me what I need/asked for in my post (from what i watched online an hour or so ago i can fast forward time and grab "new" coordinates)?

    I could also be totally wrong yet at least I've found something you have advised

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    Default Re: RA and DEC coordinates?

    A star's RA and Dec coordinates do not change. (Technical quibble: they do change very slowly over the course of years, but they do not change in the course of a night.) So, imagine that the lines of RA and Dec are drawn onto the sky, and they rotate with it.

    The setting circles on a typical GEM mount are of limited use. The RA circle, in particular, is useless until it is calibrated. And, on most GEMs, it becomes useless again a few minutes after it is calibrated. To use it, you have to point the scope at a star whose coordinates you know. Vega, for example, is at 18h38m RA (and 38deg48m Dec). You would point the scope at Vega, then adjust the RA setting circle until it reads 18h38m. For the next few minutes, the setting circle is useable. You could use it, for example, to find Deneb, which is at RA 20h42m, just by pointing the scope at 20h42m RA and 45deg21m Dec. Eventually, as you continue tracking an object, the setting circle will get left behind, and you will have to re-set it before finding the next object.

    Quote Originally Posted by Maceemiller View Post
    I am literally installing Stellarium now! I'm presuming this software will give me what I need/asked for in my post (from what i watched online an hour or so ago i can fast forward time and grab "new" coordinates)?
    When you do that, you will see that the alt/az coordinates are continually changing, but the RA/Dec coordinates do not change.

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    Default Re: RA and DEC coordinates?

    Quote Originally Posted by KathyNS View Post
    A star's RA and Dec coordinates do not change. (Technical quibble: they do change very slowly over the course of years, but they do not change in the course of a night.) So, imagine that the lines of RA and Dec are drawn onto the sky, and they rotate with it.

    The setting circles on a typical GEM mount are of limited use. The RA circle, in particular, is useless until it is calibrated. And, on most GEMs, it becomes useless again a few minutes after it is calibrated. To use it, you have to point the scope at a star whose coordinates you know. Vega, for example, is at 18h38m RA (and 38deg48m Dec). You would point the scope at Vega, then adjust the RA setting circle until it reads 18h38m. For the next few minutes, the setting circle is useable. You could use it, for example, to find Deneb, which is at RA 20h42m, just by pointing the scope at 20h42m RA and 45deg21m Dec. Eventually, as you continue tracking an object, the setting circle will get left behind, and you will have to re-set it before finding the next object.



    When you do that, you will see that the alt/az coordinates are continually changing, but the RA/Dec coordinates do not change.
    Thankyou for your reply. I'm guessing then that after polar alignment I should forget the RA circle completely and maybe just use the DEC to get me "somewhere near" to my chosen target and slowly manually move in RA both ways until I, hopefully find what I'm looking for, added with a new skill I must learn...star hopping?

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    Default Re: RA and DEC coordinates?

    Quote Originally Posted by Maceemiller View Post
    Thankyou for your reply. I'm guessing then that after polar alignment I should forget the RA circle completely and maybe just use the DEC to get me "somewhere near" to my chosen target and slowly manually move in RA both ways until I, hopefully find what I'm looking for, added with a new skill I must learn...star hopping?
    Star hopping is great if you sky will support it. It can be tough or nigh impossible in locations with heavier light pollution.

    I personally enjoy star hopping. It is a great way to become intimately familiar with the sky. Once you get a little practice with it, you may find that star hopping goes as quickly or more quickly than futzing with the setting circles.

    I like to use either a telrad or a Rigel Quickfinder to get me close to my target. After than, an optical find (RACI in my case) gets me right to my target area via star hopping. And sometimes just sighting down the OTA works.
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