Starship Asterisk*

Moons and Rings Before Saturn

Explanation: While cruising around Saturn, be on the lookout for picturesque juxtapositions of moons and rings. Another striking alignment occurred last March in the view of humanity's Saturn-orbiting Cassini spacecraft. Rhea, one of Saturn's larger moons, was caught passing Epimetheus, one of Saturn's smaller moons. Epimetheus, as pictured above, is actually well behind the heavily cratered Rhea. Further back, several of the complex rings of Saturn can be seen crossing the image horizontally. Behind both the moons and rings is giant Saturn itself, showing expansive but featureless clouds in the green light where the above image was taken. The Cassini mission around Saturn has now been extended to 2017 to better study the complex planetary system as its season changes from equinox to solstice.

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Awesome; shows the enormity of Saturn in comparison to the two moons! Well done.

What's with the happy face on Rhea?

I enjoyed the APOD, but I am confused at how the image can display in both the fore and backround the rings of Saturn with the planet located in the background. Unless Saturn is transparent. This is my first posting in this outlet. If this is not the right forum for this type of inquiry could someone help an old man find his place.

Regards, Austin Loud

Hey neufer; Rhea has a happy face because she's married to Danny Devito and they both have the same stature

nitsualoudman wrote:I enjoyed the APOD, but I am confused at how the image can display in both the fore and backround the rings of Saturn with the planet located in the background. Unless Saturn is transparent. This is my first posting in this outlet. If this is not the right forum for this type of inquiry could someone help an old man find his place.

All the rings seen in this image lie between the moons and Saturn. In order from foreground to background are Rhea, Epimetheus, the rings, and Saturn itself. The moons have a very small inclination with respect to the ring system, which is why it is possible to see them and the rings at the same time.

While cruising around Saturn, be on the lookout for picturesque juxtapositions of moons and rings.

Can't get Saturn on my Tomtom. Maybe I need a map update!

Joking aside, an amazing photo and nice to hear that the mission has been extended...

Thank you Chris L. Peterson for you timely and eloquently explained reply. I hate to impose another question for your expertise to wrangle, but I seem to be at a loss. I don't seem to yet understand how the rings that are located around the planet can be shown in front of the planet. And if I can't understand the Ringy planet thingy after your next reply I will subject myself to a life of seclusion within a cave in the depths of some ocean to alleviate the shame and humiliation inflicted through my lack of understanding , so last reply regardless:)

::sneaking in... no angel, but still fearing to tread in Chris's territory... but it's the middle of the night, so.... I'm sure he'll correct me if I'm wrong, and I'd welcome the correction, so sneak in I do...::

nitsualoudman, I think what we're seeing in this image is pieces of different rings. See here:


Epimetheus is the moon on the right; look how big the gap is between the ring(s) just "below" Epimetheus and the rings way off to the right (which I have to scroll over to see), which are barely in the picture! And Saturn isn't in the picture at all.

If you moved from this "sideways" view to the left and around so that Saturn was behind Epimetheus and you're not exactly in the ring plane, you'd see different pieces of different rings... in front of Saturn.

Does that help? Or have I muddled things completely?

Hats off to you owlice, you have made this man's day. Nicely done.

owlice wrote:If you moved from this "sideways" view to the left and around so that Saturn was behind Epimetheus and you're not exactly in the ring plane, you'd see different pieces of different rings... in front of Saturn.

You need to be careful with this image, though. It makes it appear as if Epimetheus is above the F-ring, and it is actually well outside it (i.e. this isn't a perfectly "sideways" image). Also, because the moon's orbit is slightly inclined to the ring plane, it has two crossings of that plane, so its vertical distance in any image depends on when that image was made.

But I do think your overall assessment is correct. I was looking at a high resolution image of Saturn's ring system, trying to figure out what rings are in this image. I think the lower section must be the F-ring, although it doesn't seem to have the correct structure. The more upper (inner) rings in the image really don't look like the A-ring, which should be next. They could also be part of the F-ring. It is hard to determine scale here; the lack of any features on Saturn suggests a very narrow field of view. Also, the rings are partly backlit by Saturn, which makes them appear different than when forward lit by the Sun alone.

Chris, my quotes were placed judiciously for a reason, even though it was 3:30 AM. Kudos to you for trying to figure out which rings are visible in the APOD. I considered it, looked at the rings structure for about half a second, and immediately gave up (and I'm pretty sure that wasn't because it was 3:30 in the morning... ).

nitsualoudman, glad that helped, and welcome to Asterisk!

I love this APOD; it's an astounding picture. More Saturnian lovelies can be found here, should anyone care for more.

How much longer can Cassini orbit this planet and what are the plans to galileo this machine ?

ta152h0 wrote:How much longer can Cassini orbit this planet and what are the plans to galileo this machine ?

In October 2010, Cassini will begin a new mission extension (to 2017). The mission will be renamed to The Cassini Solstice Mission (currently The Cassini Equinox Mission).

http://asterisk.apod.com/vie ... 31&t=18169

This picture is flippin unbelievably beautiful...unbelievably beautiful. Maybe there is hope for mankind afterall.
Bret

Kudos to APOD for this. Putting up with the amateur horizon pictures and nine thousand pictures of nebulae in Orion is worth it for the occasional truly spectacular and breathtaking picture like this.

Hey, if pluto's not a planet, how can Saturn's smaller moon Epimetheus be a moon?

Guest wrote:Hey, if pluto's not a planet, how can Saturn's smaller moon Epimetheus be a moon?

Pluto is a planet. And Epimetheus is a moon because any solid, natural body in orbit around a planet is a moon, regardless of size.

Pluto also has moons: Nix and Hydra, and (depending on your viewpoint) Charon. Sometimes Charon and Pluto together are treated as a binary planet.

Pluto is a planet.

Uh-uh, Chris! Are you one of those Harvard guys who get their news in a bottle?

These are the only ones of which
The news has come to Ha'vard
And there may be many others
But they haven't been discavard

Didn't you hear that Pluto has been demoted to minor planethood?



Ann

Ann wrote:Didn't you hear that Pluto has been demoted to minor planethood?

Not by me. Not by many of the other astronomers I work with. The IAU can adopt whatever definitions they like, that doesn't change the fact that "planet" is already defined by other sources, and it doesn't even require astronomers to follow their recommendations (and recommendations is all they are).

Pluto is a dwarf planet. How that can not be a planet escapes me, and apparently escapes the IAU as well! <g>

Well guys, no matter what you refer to Pluto as - if you're ever out that far on a walk, I'm sure that you are going to be looking out for it so you don't trip over it. Something about letting sleeping dogs lie.

Awesome image. In view of the huge size of Saturn compared to Rhea and that to the even smaller Epimetheus it made me think of the old fun verse:-

Bigger fleas have littler fleas upon their backs to bite em.
And littler fleas have littler fleas, and so on ad infinitum.

I just love this picture - I have to keep coming back to look at it!