Planet's positions in different reference frames

You may like to compute positions of planets in different reference frames at a given epoch and for a given observer. Of particular interest might be to determine the place in the sky where a planet can be observed. We've already defined the necessary applets which perform the single tasks to achieve this goal:

Calendar (serving as TimeBase)
PlanetOrbit
Observer
Transform
We could run several occurences of our web-browser and transfer the intermediate results manually by copy and paste. But it is more convenient to put all the applets together on a single page and to profit by their mutual exchange capability.

Example:
Compute the position of Mars in the evening sky at the third of March 1997 at 8 pm. The observer resides in Munich at longitude 11 degrees, latitude 48 degrees and at a height of 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 as planet in the PlanetOrbit applet.
Enter date and time in the TimeBase applet (the well known Calendar applet, renamed to "TimeBase")
Choose the reference frame on the right hand side to be the "Topocentric horizon system" in the Transform applet.
Activate polar coordinates.

Now perform all of these steps and scroll to the last applet called "Transform".

For the values of our example, you should finally read

0.690508... (AU) for r (distance)
77.075259... (deg) for ph
74.877452... (deg) for th
phi is the angle counted from South to East, theta the angle counted from zenith to the horizon. If you are better acquainted with azimuth A and elevation e, you may wish to calculate
A = (180-ph)
e = (90-th)

If you want to calculate the moon's position, first select the reference frame "Geocentric ecliptical system" in the left hand side of the Transform applet, and then choose "Moon" in the PlanetOrbit applet.

Zurück Dieter Egger, 1997-03-03