I thought I saw phases on Mars and Jupiter. Is this possible?

On Sun, 4 Jul 1999 you wrote:

> Monday night 6-28-99 while doing some sidewalk astronomy in Cincinnati,Ohio I
> noticed that Mars did not look round. Looking through my 12.5" f4.5 scope
> masked down to 5.25" and colimated, it appared mars had a ternimator on its
> right side. It was near its meridian and the sky was light clouds. After
> seeing this the first time I star colimated my scope just to be sure, and it
> was still there. Can this be a phase, or am I just going insane? Thanks
> Terry

Hello,

The superior planets CAN indeed show phases, although these are generally
slight departures from full. The phases are most noticeable around a
planet's quadrature, or when the sun-Earth-planet angle is 90 degrees. I
found a sketch of the phases of Mars during the 1999 apparition from Sky &
Telescupe online. The image is:
http://www.skypub.com/sights/images/9904marsback01.jpg

Jupiter also can show noticeable phases. I am uncertain about Saturn, and
the phases of Uranus and Neptune are too slight to be noticeable by any
observer on the Earth.

Thanks for writing!

Sincerely,
Kurtis Williams

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