Steve,
I have noticed the very same effect. The first time I saw it, I also
thought it was the shadow at first. I think Callisto is much darker
than the other moons, so it is much easier to see in transit, and I
think it is the only one that is *easy* to see near Jupiter's meridian.
BTW: IIRC, Callisto is also the one that exhibits the rarest events
with Jupiter, and you may have observed one of the last ones for
several years.
Bob J.
--- Steven Gottlieb <sgottlieb@telis.org> wrote:
> When I was observing at the Sierra Buttes last Thursday at a public
> star party and last night of the SF State astronomy class, there was
> a
> great shadow transit of Io (along the NEB) early in the evening. At
> the same time, there was a transit of Callisto (further north but
> initially at a similar longitude) and both the shadow of Io and
> Callisto were both prominent. In fact, I assumed I was watching the
> shadow of Callisto since it was so dark and sharply defined (several
> people found Callisto more obvious than Io's shadow), but I realized
> the next day using StarryNight Pro that Callisto's shadow transit did
>
> not begin until after Jupiter had set. In general, when I've
> observed
> satellite transits they often get lost by the time they transit
> Jupiter's meridian, so I'm not sure what to make of the observation
> of
> Callisto?
>
> Steve Gottlieb
>
>
Received on Tue Jul 27 08:10:19 2004