Hi James, Hi everybody,

----- Original Message -----
From: James Ellis <ejge@...>
To: <guide-user@yahoogroups.com>
Sent: Wednesday, May 30, 2001 2:51 PM
Subject: [guide-user] Mars diameter, undo etc


> Just planning some Mars observing for the next month and I came across the
> Horizons body information which states that the maximum angular diameter
of
> Mars is 17.9". It's disk size is currently running at 19" (correct)???
> misprint or does it mean something else?

It appears to me that 17.9" is the angular diameter of Mars when in
opposition AND supposing that the orbit of Mars is circular, with a = 1.524
AU. In fact the excentricity of Mars' orbit is such that the apparent
diameter of the planet in opposition may be comprised between 13.7" and
25.1" (this will be the case in the end of august 2003).

Some more infos (in french !) and graphics on the website of my club:
http://users.skynet.be/zmn/cab/ephem/2001/MarsOpp.htm


Laurent Zimmermann
http://users.skynet.be/zmn/cab