What is the difference between horizontal and equatorial coordinate systems apart from the notations (azimuth, altitude) and (right ascension and declination angle)? Please provide some measurements of stars with diagrams if possible and two diagrams comparing the measurements are taken by two different observers in the case of horizontal coordinate systems (since they are supposed to be relative to the observer so the measurements are supposed to be different-at least this is what i am told)
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1$\begingroup$ "at least this is what i am told" Can you expand on what you are told please. What is the context in which you are asking this question? Who is telling you about horizontal and equatorial coordinate systems? Where did you hear or read about the existence of these systems? It is good to share all your previous knowledge. It is good to do a web search first, and if there is a diagram on the web that you don't think is clear you should ask about it. $\endgroup$– James KDec 31, 2021 at 18:04
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1$\begingroup$ for example a five second search finds astronomy.swin.edu.au/cosmos/e/equatorial+coordinate+system and astronomy.swin.edu.au/cosmos/H/Horizontal+Coordinate+System I see no reason to copy those here, if you've already read them. $\endgroup$– James KDec 31, 2021 at 18:06
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$\begingroup$ I want to know why we use either over the other? Like is the horizontal one for amateur astronomy? In what sense can either be useful over the other? $\endgroup$– AveerJan 1, 2022 at 7:17
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2 Answers
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One of the biggest differences between those two is their dependency on observers. The horizontal coordinate system depends on where are you on this Earth, for example, altitude is measured from your horizon it may be different for some other person somewhere else but you will not face this problem in the Equatorial coordinate system, for example, declination is measured from the celestial equator so it will not change whichever location you go!
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You don't choose a coordinate system. If you're navigating you take sights to get horizontal coordinates, then look up the equatorial coordinates, and knowing the time, calculate your position. If you're observing some celestial body you start off knowing its right ascension and declination, and a GoTo telescope mount will do the calculations needed to point the telescope in horizontal coordinates, knowing its location and the time.
