[AZ-Observing] Jupiter and family

  • From: "Frank Kraljic" <fjkraljic@xxxxxxxx>
  • To: "AZ Observing" <az-observing@xxxxxxxxxxxxx>,"Amastro" <amastro@xxxxxxxxxxxxxxx>
  • Date: Wed, 19 Sep 2001 08:46:17 -0700

This morning I was able to push my 10" F5.5 Dobsonian near 1000x utilizing a
7mm Ortho combined with a 5x Powermate.  Surprisingly, I could still define
features on Jupiter beyond the main equatorial belts and polar regions,
including two festoons and Callisto--which I mistook for a shadow (!)--near
the southern limb.  Even Saturn's Cassini Division was apparent, however not
as crisp as I would prefer, but nevertheless isolated and visible around the
entire ring's circumference.
        At 225x, I suspected a small shadow emerging from the SSE corner of
Jupiter's disc.  Not as sharp as other shadows I've recalled observing, this
one was gray in tint and appeared diffuse around the edges.  I flipped
through Sky & Tel and confirmed my suspicion of this being not a shadow, but
the moon Callisto itself.  In the past, I've noted Callisto as having a
darker (grayer) albedo in comparison to the other moons.  To see Callisto
this dark against the Jupiter was a pleasant surprise and I do not believe a
transit occurred last apparition.  I know Callisto was not eclipsed in 2000
according to ALPO.
        Also at high magnification, I don't recall seeing as much albedo 
on Ganymede prior to this morning.  Last apparition I had sketched numerous
times the detail in the moon's surface, unfortunately, my window of
stability today lasted only a few minutes and I ended up sketching Ganymede
from memory.  I'm going to try to obtain a bitmap of Ganymede for this
morning's position through Guide 7 for comparison.
        I should also point out another feature on Jupiter I don't recall seeing
before, but is striking enough to comment.  Between the south equatorial
belt and the south polar region, the white zone between the two had a dark
band terminating near the CM at ~11:22UT, giving the appearance of an
unfinished drawn line.  I don't believe it's anything special, though.

-Frank Kraljic

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