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Bill wrote:

>Herbert:  Did you calculate your results, or is there a web site to look up
>such information?
>
I normally use MICA for this sort of thing. This is a windows program
produced by the U.S.N.O and distributed by Willmann-Bell. Last summer a
new version came out, which is good for 1800-2050. I have my quibbles
with this program, but I use it a lot and recommend it. Maybe, I post a
detailed review one day when I can find a spare minute.

Here is a website which provides similar functionality:

http://www.imcce.fr/imcce.php

>It would look like the 0.26 phase may correspond to the
>area illuminated?
>
>
Yes.

>I'm at a loss at how one derives illumination from the 117d figure.  Any
>help would be appreciated.
>
>
>
Once you have the phase angle d, the fraction of the illuminated area is
easy to compute: It is (1 + cos d) / 2. I won't attempt to give the
derivation of the formula as ascii stream, but it is a matter of simple
projective geometry if you have a picture. Consult W.M. Smart,  Textbook
on spherical astronomy, Cambridge U.P., 6th ed. 1977, p.167.

>I also wonder, if like the moon, the line/arc between illuminated and dark
>portions can be other than vertical.  If so, where can one find/determine
>that information?
>
>
Said line is not really vertical (neither is it so for the moon) but it
is perpendicular to the direction of the sun. To the extent that the
body is near the ecliptic, the line through the horns is perpendicular
to the plane of the ecliptic. If you want to know precisely, you have to
compute the angle between the ecliptic and the plane Earth-Sun-body.

Herbert Prinz

   

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