More Saturn ring awesomeness

By Phil Plait | August 10, 2009 7:00 am

Yesterday, I wrote about a weird event at Saturn, where some object apparently blasted through Saturn’s rings.

But that’s not the only cool thing that’s happened out there. As I mentioned in that post, Saturn’s rings are almost exactly edge-on to the Sun, meaning that anything that sticks out above the phenomenally flat rings will cast a long, long shadow. We’re seeing more and more of that as the rings aim themselves at the Sun — with them being exactly aligned with the Sun — the Saturnian equinox, as it were — on August 11, tomorrow!

Even now there are wonders to behold. Saturn’s narrow F ring, outside the main A ring, has been getting tortured, twisted, manipulated by the gravity of nearby moons. Whenever some event or another moves particles in the rings above or below the ring plane, they cast one of these reaching shadows. We’re so close to the equinox now that shadows fall a long way indeed:

Shadows stretches across Saturn’s rings

Check that out! Whatever that lump is that you can barely see in the F ring (I marked it with an arrow to help you see it), it’s casting a shadow over 5000 kilometers long — the width of the entire United States.

The shadow is a little faint, but that’s because Cassini was looking at the unlit side of the rings, so we’re in essence seeing this shadow literally through the rings themselves. Had the spacecraft been on the other side, the shadow would have been a lot more obvious. Incidentally, Cassini was almost 1.8 million kilometers (1.1 million miles) from the shadow when it took this image; that’s four and a half times the distance of the Moon from the Earth.

This image was taken on July 30, still two weeks before the equinox. What will we see on that exact moment, when the Sun shines straight down the knife-edge of the rings? A dozen shadows of moons as they circle hundreds of thousands of kilometers outside the rings? A vast array of parallel linear features caused by countless irregularities in the rings’ otherwise planar structure?

I can’t wait to find out! But one thing I already know: Saturn will surprise us. It has an infinite capacity for that.

CATEGORIZED UNDER: Astronomy, NASA, Pretty pictures

Comments (22)

Links to this Post

  1. abo a blog » Space | August 17, 2010
  1. Bob

    I am just in awe at the wonders of space…

    Thanks for the play by play Phil!

  2. Bigfoot

    Hi Phil,

    Thanks for pointing out the subtle-before-you-pointed-it-out shadow. It is mind-boggling to think about the length of that shodow and wonder how big the lump was to cause it.

    I eyed this image last night when you posted the ring “punch through” image:

    Although from a known source, this Daphnis shadow (an 8-KM diameter moon, although I know you know that), while much shorter, puts Don King to shame, and the 3-D ripples from the gravitational groove dance are fantastic — apologies if you posted this before!


    Phil, you forgot to say: “Click on the image to embiggen”! 😉

  4. Jay

    The pictures are amazing even without any context, but when you start thinking about the sheer scales involved, it gets absolutely mind boggling.

    Great stuff, Phil!

  5. Actually, equinox is today here. It’s at 00:15 UTC on the 11th, so it’s around 5-8 PM in most of the US. (Sorry Alaska and Hawaii. I can never remember your time zones.)

    I baked a (dark chocolate) cake to celebrate. Really.

  6. Bill Nettles

    How big does that thing have to be to case a 5 Mm shadow before diffraction kills the shadow? I guess the umbra is shorter than the diffraction length, but what about the penumbra?

  7. Gary Ansorge

    Ooh,Ooh, looking at the really embiggened pic, you can see ripples in the shadowed portion of the ring. Looks a lot like the harmonic oscillations of a guitar string,,,(JERRY, I KNEW you were still around,,,)

    Now we can tell DeadHeads around the world that Garcia is hanging out at Saturn, playing the Rings,,,(Gee, I wonder what they sound like?)


    GAry 7
    That’s a whole lot more fun interpretation than Hoagland is likely to come up with,,,

  8. That is just simply amazing!

    Dr. Plait, still wondering about the wide field of view telescope question from yesterday’s post (#11). After all, it applies directly to your book, so I figured you’d want to answer that. :)

    Yeah, who knew, he wrote a book!

  9. Diffraction is wavelength dependent. Usually, if your object is much larger than a wavelength, diffraction isn’t much of an issue. So if the feature is larger than maybe a few microns (and it certainly is*), you’re fine.

    * The umbra wouldn’t reach all the way out if it were that small. The ratio of how far the umbra exists to the radius of the body is 2,200 at Saturn. This actually probably provides a better constraint: if we are seeing an umbra (and not a penumbra) all the way out, the feature must be at least around 3 km in radius.

  10. FenrirKar

    I TOLD you it was Frank Poole!

  11. Evil Eye

    What has Caroline Porco had to say about all these weird shadows?

  12. Torbjörn Larsson, OM

    My thoughts exactly, what has Saturn Shadow Master Porco seen since last time? (Sounds like she’s practicing ninpō, doesn’t it?)

    It has an infinite capacity for that.

    Ideally perhaps. Physically, I’m sure it isn’t even unbounded over infinite time if seen in isolation. AFAIU you need an open system for that. And don’t get me started on finite time. 😀

    Have I told you how much I absolutely positively detest infinitely inflated hyperboles? Or at least feel the competition to keep up? 😉 Oh, and get off my lawn! [/rant off]

  13. Gary Ansorge

    So the object casting the shadow, from the width I see, would appear to be about 50 km wide?

    Considering the resolution, that’s a pretty amazing pic,,,

    GAry 7

  14. XMark

    Saturn seems to be the planet with the largest number of awesome doodads and thingamabobs circling around it.

  15. TS

    I used to be able to recognise a song just by looking at the grooves on my records and I’m definitely seeing Bad Moon Rising by Creedence Clearwater Revival”.


  16. Plutonium being from Pluto

    Talking about casting a long shadow! That’s just awesome. 8)

    Thankyou Cassini – & thanks too BA.

    Looking forward to the images of the moment itself … :-)

    BTW. Question – has Jupiter or Saturn got the most moons in our solar system? Which planet holds that record?

    BTW. My planet Pluto’s not doing too badly there – we’ve got Nyx , Hydra and the largest moon in relation to planet size – Charon -plus rings of our own. As you’ll see when New Horizon’s flies past in 2015. You won’t see us Plutonium beings through – we’re deep under the Plutonian ice in the ocean near the molten core! 😉

  17. MJKelleher

    @John Weiss #5
    Actually, equinox is today here. It’s at 00:15 UTC on the 11th, so it’s around 5-8 PM in most of the US. (Sorry Alaska and Hawaii. I can never remember your time zones.)

    I think the good doctor was referring to equinox for Saturn, “when the Sun shines straight down the knife-edge of the rings”. I’m looking forward to some amazing photos from then!

  18. Jeff

    well, it must be a particle of some size, maybe they could calculate the size, maybe km.

    so saturn’s rings aren’t solid after all, they do consist of myriad particles, like that was a surprise

    Also, the two sides of the shadow are virtually parallel over 5000 km, which speaks of the parallel nature (nearly) of the solar rays at saturn’s position (10 AU). If the sun subtends an angle of 0.5 degrees at earth, it should subtend 0.5/10 = 0.05 degrees at Saturn, which is why the shadow is so uniform .

  19. Mount

    Obviously the only thing that could have blasted out of the F-ring and made that kind of disturbance is an alien mothership! It’s the only thing that makes sense!!!! When will NASA stop ignoring the proof?!!?!?


  20. coolstar

    Might this be a good time to point out the difference between equinox on Saturn and a ring plane crossing, as seen from the earth? The next rpx occurs on Sept. 4. The difference is because Saturn’s orbit is inclined by about 2.5 degrees to the orbit of the earth, the ecliptic. Thus ring plane crossings typically occur more frequently than do Saturnian equinoxes.

  21. bob

    the best website ever


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