Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How do you calculate declination and Right Ascension from Earth Coordinates?

  1. Sep 29, 2012 #1
    Say a person is positioned here: 40.23°N and 15.89°E and was examining the night sky.

    How do you calculate the declination and Right Ascension from that location's coordinates?

    I know the RA is measured in hours up to 24 and Declination in degrees.

    Any ideas?
  2. jcsd
  3. Sep 29, 2012 #2


    User Avatar
    Science Advisor

    Your question doesn't make much sense. Declination and Right Ascension are coordinates of a point on the sky. So it depends not on where you are on Earth, but on where in the sky you are looking. At any time, you can see half the sky, so you could be looking at a wide range of RA and Dec coordinates.
  4. Sep 29, 2012 #3


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Hi Brynjolf

    welcome to PF :)

    yes I have to agree with physguy on that one. Starmaps/atlases are produced showing RA and Dec co-ordinates of the sky. You are able to use that star map anywhere in the world without having to do any conversion.

    The only thing that varies is whether a particular RA and Dec co-ordinate is above or below your local horizon at a given time of the day/year from you current location

  5. Oct 9, 2012 #4
    Straight up Azimith = 0 and Altitude = 90 at":

    RA = LMST

    DEC = Latitude = 15.89°E

    LMST (Local Mean Sidereal Time = GMST0 + time * 15 + Longitude)
    GMST0 (Greenwich Mean Sidereal Time at Midnight)

    Last edited: Oct 9, 2012
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook