Comet's positions in different reference frames

You may like to compute positions of comets 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 comet can be observed. We've already defined the necessary applets which perform the single tasks to achieve this goal:

Calendar (serving as TimeBase)

CometOrbit

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.

We have neglected the influence of precession for the time span between J2000 (the epoch of the orbital elements' reference system) and the actual epoch of date. You may check the TimeLink-page and see that the precession angles are indeed very small nowadays (about one minute of arc).

Example:
Compute the position of Hale-Bopp in the evening sky at the 20th of March 1997 at 7:30 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 Hale-Bopp as comet in the CometOrbit applet (may be skipped)

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

1.31611... (AU) for r (distance)

218.04201... (deg) for ph

74.08499... (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 (= 321.95799 for the example)

e = 90 - th (= 15.91501 for the example)

Dieter Egger, 1997-03-13


	Enter the observer's coordinates in the Observer applet and hit Return.
	Choose Hale-Bopp as comet in the CometOrbit applet (may be skipped)
	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.