Dieter Egger @ FESG TUM
Planet's position in different reference frames
Compute the position of the Sun, the Moon or a planet in different reference frames at a given epoch and for a given observer.

The applets

  • Calendar (TimeBase)
  • PlanetOrbit
  • Observer
  • Transform

will do the job.

Of course you might run several occurences of your web-browser including the corresponding applets (one per browser) and transfer the intermediate results manually by copy and paste.
But it is much more convenient to collect the applets on a single page and thus to profit by their mutual communication capability.


Compute the position of Mars in the evening sky at the third of March 1997 at 8 pm (20:00 UTC). Assume the observer to reside in Munich (longitude 11 degrees, latitude 48 degrees, height 550 m above sea level).

The following steps will solve the problem:

  • Enter the observer's coordinates in the Observer applet and hit Return.
  • Choose Mars in the applet PlanetOrbit.
  • Enter date and time in the Calendar (TimeBase) applet
  • In the Transform applet choose "Topocentric horizon system" as target reference frame (right hand side).
  • Select polar coordinates.

Maybe that you have to repeat one of these steps in order to get correct results (Netscape 6.2 did not function properly)

If you have been entering the values of our example, you should now read

0.690508... (AU) for r (distance)
77.075259... (deg) for ph
74.877452... (deg) for th

phi is counted from South to East, theta is counted from the zenith to the horizon.

To get azimuth A and elevation e, just follow the steps

A = (180-ph)
e = (90-th)

Remark: To calculate the position of the Moon, first select the reference frame "Geocentric ecliptical system" as source reference frame in the left hand side of the Transform applet before selecting "Moon" in the PlanetOrbit applet.


Dieter Egger,  last update 2002-02-27