Re: ATM Another optics test - Jupiter's moons

["Dan Chaffee" <dchaffee@gvi.net>]

> Here's the question:  As a way to evaluate optics/observers/seeing
> conditions, are all the gallilean satellites equally easy/hard to see 
> transiting the face of Jupiter?  If not, which ones are easier than
> others?  What's the smallest scope aperture you would need to see a
> moon against the backdrop of Jupiter?

Tom,
Perhaps the question is a bit more complex . When a galilean satellite is near
the edge of the planet it becomes much more visible due to the darkening
of the disk near its  perimeter. A much smaller aperture can pick it up at such
a location than when a moon is within say, 15-18 arcsec. from the central meridian
(given that Jupiter is presently 48.6 arcsec. dia.).
Also, since contrast is really the issue, the aperture required would likely be related
to whether or not it's obstructed.
It's an iteresting question and with this in mind, I'd also like to know.

Dan Chaffee