It make sense that there would be no shadow showing on the rings right now
because we are so near Saturn's opposition, by the very nature of light from
the sun traveling on a line very near the earth out to Saturn. Kind of like
a straight pole standing perpendicular to the earth at noon on the equator
during the equinox would cast no shadow. There is an article on page 105 of
the December 2003 issue of Sky & Telescope (a caption really) that talks
about the shadow that appears on the rings of Saturn and how it switches
sides around the date of opposition.
Dec 1, 2003 prior to opposition shadow appears off of the left limb
Dec 31, 2003 opposition shows no shadow
Feb 1, 2004 post opposition shadow appears off of the right limb
approximately Mar 20, 2004 shadow off of right limb is at it's widest before
it start to thin again
Casey
----- Original Message -----
From: "Peter Natscher" <natscher@No-Spam>
To: "[TAC]" <sf-bay-tac@No-Spam>
Sent: Tuesday, December 30, 2003 4:21 PM
Subject: [TAC] Saturn's Shadow On Its Rings At Opposition Time?
> 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
>
>
