Saturn brain bender

By Phil Plait | October 6, 2010 7:00 am

Usually, pictures of Saturn aren’t too hard to figure out. Planet, rings, moons, and so on. But then this picture showed up, and I had a real What the frak?* moment:


I have to admit, it took me a few seconds of disorientation before suddenly the picture geometry snapped into my brain. It was like one of those optical illusions where once you see it, you can’t not see it!

So what’s going on here? Actually, a lot! So strap yourself in.

Basically, Cassini was behind Saturn when it took this picture; the sun, Saturn, and Cassini were almost exactly all on a straight line (for pedants, the Sun-Saturn-Cassini angle was 178°). From Cassini’s point of view, Saturn was almost completely unilluminated by the Sun. In others words it was over the night side of the planet.

The Sun is shining down on the rings a bit, and Cassini is viewing them from underneath. Off to the right, you’re seeing the rings with sunlight scattering through them. The dark triangle is Saturn’s shadow on the rings. The curved line of the triangle on the left is the limb of the planet.

So what’s with the rings on the left? Is that the shadow of them on Saturn? Nope, it can’t be, because the Sun wasn’t lighting them up. So those must be the rings themselves in silhouette! The lit-up part of the rings on the right reflect light onto the dark side of Saturn, illuminating it a little bit. That’s why you can see the disk of the planet at all. But the rings go all the way around, and on the upper left, they block that small amount of light coming from the planet.

OK, fine, then what’s that weird faint glow on the planet then just below the silhouetted rings? Ah, that’s light scattered from Saturn’s own atmosphere! After the Sun sets on Earth, the sky is still lit up a bit, right? It’s only when the Sun is well and truly set, about 90 minutes later, that it gets completely dark. That’s because sunlight hits the Earth’s air and bounces around, letting it light up the air a bit on the dark side of the Earth.

Same thing here on Saturn: that glow is a little bit of sunlight that got scattered by air closer to the lit side of the planet, and it gives the dark side a taste of light. I guess you could say that if you were floating in Saturn’s atmosphere, at that point, it would be twilight for you. And if you looked up, you’d see the magnificent rings coming across the sky, then suddenly cut off by Saturn’s shadow. What a sight that would be!

Still having a hard time? This may help. Remember this glorious picture of Saturn from 2006?


This is a mosaic of quite a few images, stitched together to produce this magnificent portrait. The Sun is behind the disk of Saturn, and you can see the rings lit up on the sides, but in silhouette against the disk itself.

Now imagine the shadow of Saturn is cutting off a piece of the rings:


I Photoshopped in the shadow (I know, the angle is all wrong, but this is supposed to be illustrative, not perfect), and then put a red box around the region showing, more or less, where the new image is (I also flipped the original full-Saturn image around so that it better matches the new image). Now do you get it? We see the lit rings on the right, the shadow of Saturn across the middle, and the silhouetted rings against the disk of the planet! Mind you, this isn’t an exact match, and what I did was very crude and not terribly accurate, but I hope it’s more — wait for it, wait for it — illuminating.

Very cool. I remember when the Voyager probes passed Saturn back in the early 80s. The pictures were incredible! We learned a lot, and it inspired a generation of would-be astronomers (including me). But those spacecraft flew by Saturn at high speed. Now we have Cassini orbiting Saturn, as it has so many times since 2004, and with that residence comes views like this. It’s what happens when you plan to stick around a while.

* Given that my friend Kevin Grazier is on the Cassini team, and was also science advisor for Battlestar Galactica, it was not just recommended, but required, that I use this phrase. So say we all!

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (48)

  1. Jason

    That is a very cool picture, All of them are. It is amazing what a beautiful universe we live in. Even if it is occasionally “bad” :)

  2. highnumber

    Phew! I was thinking that shadow was a monolith. Thanks for explaining.

  3. Messier Tidy Upper

    I love <3 these images. Thankyou Cassini & thanks phil for sharing them. :-) 😀

    Nice write up and great photoshopping job to explain that first one too, thanks BA. :-)

  4. Monkey

    Phil, sometimes you make my jaw drop. The picture, stunning. But your words make the picture stunningly amazing. Keep typing dude….love it love it love it…..

  5. Jason

    @2 highnumber — wrong planet.

    Just stay away from Europa. Though, I wonder if Titan would work as well as Europa, though a different bio-chemistry.

  6. I love the little footnote. :)

    @Jason (5), probably not if the same mechanic was used. If we turned Saturn into some sort of sun of any magnitude, Titan’s oceans and probably atmosphere would boil off pretty fast.

  7. Gary Ansorge

    It jus goes to show, Carbon based life forms get all over EVERYTHING.

    ,,,or, as a bunch of DeadHeads used to say,,,WE ARE EVERYWHERE.

    Great pic, Phil.


    Gary 7
    PS my Son sent me a follow up on the Gliese 581 planet. The scientist that discovered it (Vogt) indicated it probably has a surface G of about 1 to 1.5. I could handle that,,,

  8. Jason

    @6 Larian Good point.
    I had forgotten just how … volatile Titan was.

  9. Messier Tidy Upper

    Remember this glorious picture of Saturn from 2006?

    I’ll never forget it! That backlit ringed planet (with hidden Earth caught in the rings I gather) is my all time fave image seriously challenged for the top honour only by this superb one :

    of spiral galaxy Messier 66 as it would look if you were flying just above it. :-)

    That picture of Saturn backlit is just glorious. I want it as a poster, a mural, a gigantic billboard over the road! :-)


    PS. Phil, have you ever considered releasing a calendar of some of the images you’ve posted here? Seriously, I’d buy one. :-)

  10. Jason

    @7 Gary
    Isn’t he also the one who said he is certain it has life?

    Or am I just misreading misquotes from a media that really doesn’t understand science and is throwing out sensational headlines?

  11. chris.j.

    in the book version of 2001, it’s saturn, not jupiter, so highnumber has reason to be wary.

    ironically, i remember hearing that the movie for 2001 switched the scene to jupiter because they couldn’t do saturn’s rings with f/x (and back then, i don’t think they knew jupiter had a ring too).

  12. Messier Tidy Upper

    @7. Gary Ansorge Says:

    PS. my Son sent me a follow up on the Gliese 581 planet. The scientist that discovered it (Vogt) indicated it probably has a surface G of about 1 to 1.5. I could handle that,,,

    Getting a little off topic here sorry – & also apologise for being a wet blanket here but what is Vogt basing that statement on?

    Given Gliese 581 g or “Zarmina” as he and I prefer to call it, has a mass that is triple – at minimum and even possibly quadruple – that of Earth’s I’m afraid I wouldn’t be so sure of that figure. :-(

    Bear in mind too that it was presumably this same Vogt who earlier made the rather silly statement :

    “The chances for life on this planet are 100 percent,” Steven Vogt, a UC professor of astronomy and astrophysics says. “I have almost no doubt about it.”

    [NB. quoting this from comment # 135. drksky on that last Gliese 581 g news BA blog thread.]

    Or was quoted as saying that anyhow. So, hmmm…

    My confidence in what Vogt says is low and accompanied by a sizeable shaker of NaCl* also known as halite and best known as salt. 😉 :-(

  13. Jason

    @10 Chris.j

    I don’t remember. I’d have to look it up, its been a very very long time since I read those books

  14. Whoa! Beautiful and amazing!

  15. Calli Arcale

    Jason @ 5:

    Actually, monoliths at Saturn aren’t necessarily wrong. In the book “2001”, the monolith is actually on Iapetus (which Clarke spelled “Japetus”). Kubrick switched over to Jupiter orbit (with Clarke’s blessing) when the FX team found it impossible to depict Saturn’s rings to their satisfaction. The glass painting method used so exquisitely for Earth, the Moon and Jupiter just couldn’t make the rings look right, and ultimately a setting change was the simpler solution.

  16. Messier Tidy Upper

    Pretty sure in the original Arthur C. Clarke novel ‘Space Odyssey 2001′ the Monolith was actually located on Saturnian moon Japetus, now better known or spelt as Iapetus.

    The Kubrick 2001 movie placed then placed the Monolith freely orbiting Jupiter instead and the subsequent Space Odyssey novels continued with the Jupiter idea and so were technically sequels to the movie and NOT the original text! 😉

    Of course, the very first monolith was dug up from Tycho crater on our Moon (or going even further back was located in prehistoric Africa) and then there’s the original short story ‘The Sentinel’ which Clarke wrote preceeding the novels.

    I think I also read Clarke saying somewhere else that each of the novels and the novel was set in an alternate subtly different reality of its own! Which is kind of the ultimate retcon. 😉

    I could, of course, be wrong & would have to check myself but am pretty certain of this.

    [ Still waiting for this year’s expected transformation of Jupiter from gas giant planet into our solar system’s second star. What’s that I hear about it being only fiction .. Heresy! 😉 ]


    EDIT : & I see Calli Arcale has just beaten me to it. Oh well. :-)

  17. Jeff

    This is the kind of stuff that keeps me coming back for more at Phil’s blog. I don’t know anywhere else where I can in 2 minutes with my morning coffee get the “skinny” on all the new stuff in solar system exploration, plus with Phil’s expert and easy to understand commentary.

    thanks for being there. I don’t even get as much knowledge from my colleagues next door as I do from these kind of blogs

    This is so much better than just going to any science website and reading articles by who knows who they are. Maybe they are just staff writers with basic high school science but no expertise in science.

  18. Messier Tidy Upper

    See more also via Wikipedia pages for the Monoliths :

    and the series of novels, films and short story singular :

    and also for Iapetus

    which confirms its occassional alternative spelling of Japetus and also even more rarely & archaically Saturn Five as well.

    Hope this is interesting / useful / enjoyable for y’all. :-)


    “The Ramans do everything in threes.”
    – Arthur C. Clarke, ‘Rendezvous with Rama’, Final page (252), Pan
    Books Ltd, 1973.

    @ 19. Jason : No worries. :-)

  19. Jason

    @calli15 & @16Messier
    Thanks, I didn’t remember all that.

  20. Gary Ansorge

    10. Jason


    12. Messier Tidy Upper

    It helps to have read the entire interview(here).

    I agree with his optimism. Since the rocky planet is in the “life zone”, I would also bet for life, rather than against it.

    That stuff gets on EVERYTHING,,,

    Gary 7

  21. Grand Lunar

    I thought I had this figured out before reading the description you gave Phil, but saw I was wrong one at least one point.
    I thought the silhouette was a shadow, cast by moonshine.
    I didn’t think the light from the rings themselves would cause that appearence. Nice one!

  22. The Mutt

    I think Cassini’s camera strap was hanging in front of the lens.

  23. Huh… very enlightening.

    Cool stuff.


  24. One thing I’ve always wondered about Saturns rings – are they dense like dirt? Could you “swim” in one? Or are the bits of matter yards apart and just look solid from a distance?

  25. Mapnut

    Are you guys all praising the emperor’s new clothes? Or does everybody but me get how you can see rings in the shadow of Saturn and at the same time see a shadow that’s completely black? And how come the shadow ends at the limb of Saturn if it’s Saturn’s shadow? I don’t get Phil’s diagram, or verbal explanation either. In other words, I’m still at “what the frak?” I don’t suppose it’s possible to get a view of the subject photo, panned back. Is there a similar photo of the shadow on the rings that would help me? Is this maybe a composite photo with two exposures?

  26. Jason

    @24Dan S.
    A quick Google turned up the following abstract

    ” Corresponding mass densities are 32–43 kg/m2 in ring C, 188 kg/m2 in the Cassini division, and 244–344 kg/m2 in ring A, under the assumption that the material density of the particles is 0.9 g/cm3 ”

    Howard A. Zebker, Essam A. Marouf, G. Leonard Tyler, Saturn’s rings: Particle size distributions for thin layer models, Icarus, Volume 64, Issue 3, December 1985, Pages 531-548, ISSN 0019-1035, DOI: 10.1016/0019-1035(85)90074-0.

  27. Sort of an Escher take on Saturn.


  28. Phil:
    I hate to disagree with you (but this happens all the time in science, dunnit?) but I think “that weird faint glow” is ringshine. Light from the Sun is bouncing off the top of the rings and hitting the atmosphere. If atmospheric scattering (twilight) was the cause, then there’d be that much glow at the bottom of the image as well. There -IS- a tiny bit of that twilight visible at the edge of the planet’s limb, though.

    It took only a couple seconds for me to properly orient myself when I first saw this image today. Probably comes from being a videographer and astronomer all rolled into one, I guess. When I watch TV or movies I always look at shadows and try to determine where the light sources are. I’ve always been a big fan of:

    Whattaya thingk?

  29. Now that I read your entry more carefully, I think you might have been referring to the little line of twilight when you said “that weird faint glow” after all… I should’ve read it more carefully the first time! Gaak!

    There is, however, a tiny bit of something going on at the very top of the image, a nearly vertical bit of something grey that follows the curve of the limb… This image just keeps on giving!

  30. chris.j.

    Mapnut and Richard Drumm, i think both of you are seeing the effects of processing on the image. logically, scattered light from the rings will illuminate saturn’s night side, as is easily visible here, but that backlighting will in turn illuminate (albeit faintly) the part of the rings in saturn’s shadow. in a raw photo, i suspect that after-after-glow might be barely visible, but i think this image has been enhanced to bring out the detail of the lit rings and the rings blocking saturn’s disk.

    in other words, light hits ring ice that is “behind” saturn’s terminator (directly over a part of saturn that is not lit directly by the sun), and bounces off the ice and onto saturn’s night side. some of that light bounces again onto the rings, but at this point it’s too faint to see and is presumably processed out to enhance other, more visible details.

    i also suspect that this image was taken closer to saturn’s spring/fall equinox than the prior, majestic “panaroma” picture, as there seems to be less ringshine than in the other picture.

    the smudge at the top left appears to be either a processing smudge, or perhaps a blur caused by the craft’s motion (or both).

  31. Chris S

    After understanding this photo – great explanation! – I think I found an additional hint to help in future.

    You state: But the rings go all the way around, and on the upper left, they block that small amount of light coming from the planet.

    However – if you imagine the rings of the right continuing into the shadow region, you can see that when the reach the edge of the planetary disc, the bright and dark rings don’t match. That’s the extra big clue that one set of rings is illuminated directly by bright sunlight, while the other portion is illuminated with dim darkside planetshine.

  32. Nullius in Verba

    You can set the shot up in Celestia in less than a minute.

    Load the program, type ‘6g’ to fly to Saturn, drag with the right mouse button to place yourself on the other side of the planet below the rings. Zoom out a bit with the mouse wheel to see how it works.

    Yes, the shadow geometry is all wrong, which makes the picture fairly incomprehensible. A Celestia screenshot would be clearer, or you can use the program yourselves to spin it round in 3d for the ultimate ‘day trip to the stars’ experience.

  33. Jonathan H

    @26. Jason
    Could you dumb that down a bit? The only number in there that I think I understand is “0.9 g/cm3”, which compared to water’s 1 gram per cubic centimeter suggests that you actually could swim in them.

  34. Nullius in Verba


    According to #26, the A ring has an area density of about 300 kg/m^2, and the rings are about 10 m thick, so the density is about 30 kg/m^3. If it was solid ice, it would be 900 kg/m^3, so we’re talking about 3% of the space being filled. The C ring is a lot thinner.

    Or to put it more simply, the same density as a couple of ice cubes in a pint glass.

  35. Tribeca Mike

    I’m stupified, startled and dumbstruck. Thanks for the fascinating photo and info.

  36. Jeremy Thomson

    You did more than photoshopped the shadow. You flipped the image so thats instead of the glint of sunlight at the terminator being at the bottom and leftish its now at the top (and leftish).

  37. Jason, Calli, MTU:
    Correct – the film version of 2001 changed the setting to Jupiter, because the special effects people couldn’t produce a convincing Saturn.
    Now consider that
    a. The film used absolute state of the art special effects for its time, and
    b. It was produced at the very same time as the Apollo missions were being planned ( released in 1968, the year of Apollo 8 ).
    A point to make to all the conspiracy morons who claim that “this and that could easily have been faked” in the Apollo footage, and don’t realise that we didn’t have the same technology 40 years ago that we do now! DUH!!!

  38. molybdenumfist

    I thought I had got it until Phil’s Photoshop skilz threw me for a loop.
    Setting it up in Celestia makes it pretty clear, thanks Nullius.

  39. mfumbesi

    What a sight it would be indeed.

  40. Nemesis

    Amazing photograph!

  41. mike burkhart

    The moon is a big source of optical illusions . I’ve read about an amture astronomer in the 1950s saw thro his telescope what appered to be a bridge across the Mare Crisium that later dissapered he probally saw shados made by the bolders on the rim (why Aliens would build a bridge there in the frist palce dosen’t make sense the dark areas of the moon are call seas only because early astronomers thought they were bodies of water , now we know there is no water in the moons seas) the man in the moon is the bigest illusion , also there are claims of a grate wall again made by shados . By the way the resion the monolith in the novel 2001 was at Saturn was orginaly that part of the movie was to take place there, it was changed to Jupiter because the special efects and artwork were cheaper for Jupiter then Saturn the rings gave them problems but the special efects director Douglas Trumble made a film called Slient Runing in the 70s that took place at Saturn and found an efect for the rings when the spacecraft gos thro them.

  42. Tribeca Mike
  43. that stuff about global warming is part fact! every single planet is heating up at the same time. I mean what is it about the sun spot cycle you nerds don’t get? snap out of your bunk science, because the IMF wants to tax carbon! That means tax everything Breathing, cooking, GPS devices in our cars to tax you by the mile on top of buying the other slave maker OIL! I hate oil! but saying alternative energy is “GREEN” simply implies global warming is 100% man made! call it Tesla tech or something. Globalisation of our economy leads to a loss of freedom and global carbon tax is not the answer even if humans cause climate change. So look up Eco Science written by Obama’s science czar! the book openly talks about slowly killing off population in order to “help” the planet from the human “bomb”! Thats why we have GMO food which is proven to sterilize lab mice after 3 generations, and make their genitalia turn black and blue! but awww it’s so good for earth right. just drink your flouride water and shut up!

  44. Jim A

    I was confused because the dust on my monitor looked like stars where the ring was in shadow. I was trying to figure out how I could see stars and not rings.

  45. Hello and thank you Phil.
    When someone does a great job, with a very little mistake in it, it would be better to
    eliminate that little mistake, and have a greater job.

    Okay….. I mean the “added shadow” in the third picture.
    If I am right (and please tell me if not), the shadow must be visible only on the
    rings and not all the way out.
    Of course, the “illuminating” does work for our brains, but the shadow is extended too much!!!

  46. I shall consider my mind blown


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