I think the seeing plays tricks with planetary detail at the eyepiece. The
HST images aren't affected by the earth's atmosphere. The two "ears" are an
optical illusion in the area of the Cassini Division meeting the darkened
limb of Saturn's globe.
Peter Natscher
> From: Raymond Duval <rpduval@No-Spam>
> Reply-To: The Astronomy Connection <sf-bay-tac@No-Spam>
> Date: Tue, 30 Dec 2003 17:09:42 -0800
> To: The Astronomy Connection <sf-bay-tac@No-Spam>
> Subject: Re: [TAC] Saturn's Shadow On Its Rings At Opposition Time?
>
> I still think it was just an optical illusion - the Cassini division
> was in just the right place to make it look like shadows just below
> where it meets the planet's outer edge. IOW, just an apparent bending
> of the light. Not sure if my opinion counts, being a rookie and all,
> but that's what I saw through Dave's scope.
> RPD
>
> On Tuesday, Dec 30, 2003, at 16:21 US/Pacific, Peter Natscher wrote:
>
>> 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
>>
>>
>
>
