I'm new to astronomy and have to make a star map that displays the stars above a current location. From the information I've pieced together I understand that declination is equal to the current latitude of the observer, however I am slightly confused about right ascension. My two quesions are;

  1. If I work out GMST using the equations here; http://www2.arnes.si/~gljsentvid10/sidereal.htm will the answer be the current right ascension above Greenwich or are there more steps I've missed?
  2. If I want to find the sidereal time of, for example, Sydney, Australia, do I need to account for daylight savings at either location or do I simply add 11 hours to GMST?

Thank you for your help.


1 Answer 1


I can't vouch for the formula, but you can try it out and check with some internet source, eg USNO, to see if it works. If the formula is correct, that's it.

As for the sidereal time in Sydney, you need the difference in longitude between Greenwich and Sydney, and use the conversion rate of 15 degrees longitude is equivalent to 1 hour.


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