In further response to the conversations between me and David Kingsley on
Saturday night at Fremont Peak when we were observing Saturn, whether Saturn
was showing a shadow from its globe onto its rings, I don't see any shadow
when carefully examining Hi-res HST mages of Saturn at opposition. During
the days around Saturn's opposition, the visually observed darkening that's
noticed at the junction of the globe and rings behind the globe is only the
darkened limb of the globe and not a shadow. Like Jupiter, Saturn exhibits a
darker limb as compared to the brighter central area of the globe. Take a
careful look at a HST Saturn image taken during opposition time at the HST
Saturn Image website.
http://hubblesite.org/newscenter/newsdesk/archive/releases/2001/15/image/a
What do you think?
Peter Natscher
Monterey
______________________________
David Kingsley wrote:
......
Saturn was
absolutely beautiful last night at magnifications up to 450x The
crepe ring was very obvious all around the planet, with lots of other
structure and brightening in the A and B rings. Beautiful banding
was also visible on globe. While soaking in the views, I was
surprised to see two dark ears poking out behind the planet where
Saturn's edge was superimposed over the ring behind it. Each small
black ear almost identical in size. While looking at this, I thought
it must be the shadow of the planet projected on the rings. However,
a shadow could only produce symmetric black ears if Saturn was very
near opposition. I subsequently checked Karkoschka's handy atlas,
and sure enough Saturn last night was only a few days away from its
opposition on December 31st, 2003. I have previously watched the
shadows of Jupiter's moons switch from the preceeding to following
side of the tiny moons as Earth caught up with and passed the king
of planets near opposition
(http://www.observers.org/reports/2000.11.27.html). Saturn's rings
make it possible to see a similar effect with the shadow of an entire
planet. The two symmetric black ears were an interesting bonus to a
wonderful view. I suspect that by the time that I get a chance to
look again, the shadow on the following side will start to grow as
the earth pulls away from Saturn after opposition.
(for anyone who wants to see an image of the symmetric black ears
effect, there happened to be a post today by someone on the AP-user
Yahoo group who imaged Saturn imaged last night with an 8 inch F/15
AP. The views through both the 14.5 inch and 20 inch starmaster last
night at Fremont Peak, were actually somewhat sharper than what was
recorded in the image, but it gives you some idea of the detail
visible in moments of good seeing last night , and the two black
ears. Unfortunately, you may have to joint the yahoo group to see
the file
http://groups.yahoo.com/group/ap-ug/files/17Saturn12-27-03.jpg )
......
Happy new year, and best wishes to both new and old observers in 2004.
David Kingsley
