From decwrl!elroy.jpl.nasa.gov!usc!cs.utexas.edu!uunet!allbery Fri Apr 27 19:11:55 PDT 1990
Article 1495 of comp.sources.misc:
Path: decwrl!elroy.jpl.nasa.gov!usc!cs.utexas.edu!uunet!allbery
From: downey@cs.umn.edu@dimed1.UUCP
Newsgroups: comp.sources.misc
Subject: v12i015: ephem phase correction
Message-ID: <86191@uunet.UU.NET>
Date: 25 Apr 90 22:39:27 GMT
Sender: allbery@uunet.UU.NET
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Approved: allbery@uunet.UU.NET (Brandon S. Allbery - comp.sources.misc)

Posting-number: Volume 12, Issue 15
Submitted-by: downey@cs.umn.edu@dimed1.UUCP
Archive-name: ephem4.13/patch01

This is a correction to ephem related to calculation of phase (percent
illumination). All posted versions of ephem to date (up to and including 4.13)
calculate phase correctly only for objects in the ecliptic. Note that the
problem is particularly evident with comets.

The fix is just one line in circum.c. Change the line that reads:
	    f = 0.5*(1+cos(lam-lpd0));
to be:
	    f = 0.25 * (((rp0+rho0)*(rp0+rho0) - rsn*rsn)/(rp0*rho0));

It is a simple enough change that I did not make this an automatic patch of
any sort. The exact line number changes with different versions but the line
is unique and unchanged in all releases.

Sorry for the problem. Please contact me if you have any questions.

Elwood Downey
downey%dimed1.uucp@cs.umn.edu, or
uunet!rutgers!umn-cs!dimed1!downey