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October 22, 2007

Rainbows in the Rings of Saturn
Posted by Teresa at 05:45 PM * 67 comments

Rainbows in the Rings

As seen from Cassini. To quote Tim Kyger, who sent me the photo, that’s “one hell of a big diffraction grating at work.”

Comments on Rainbows in the Rings of Saturn:
#1 ::: Stefan Jones ::: (view all by) ::: October 22, 2007, 06:01 PM:

No dancing unicorns, though.

#2 ::: David Wahler ::: (view all by) ::: October 22, 2007, 06:08 PM:

Phil Plait says it's not diffraction, just an artifact of the imaging process — the probe moved in between taking the three successive color components.

#3 ::: abi ::: (view all by) ::: October 22, 2007, 06:09 PM:

Somewhere over the ringbow
In the Black
There's a world that I read of
Published in paperback.

Somewhere over the ringbow
Stars shine bright
Mankind spreads through the cosmos
Crossing the endless night.

Someday I'll wish upon a star
And wake up wher the Earth is far
Behind me.
Where troubles melt like comet tails
Away among the solar sails
That's where you'll find me.

Somewhere over the ringbow
Starships fly
Ships fly over the ringbow
Why then, oh why can't I?

If aliens and spaceships fly
Beyond the ringbow
Why, oh why can't I?

#4 ::: David Wahler ::: (view all by) ::: October 22, 2007, 06:29 PM:

It is an awesome picture, though.

#5 ::: Hamilton Lovecraft ::: (view all by) ::: October 22, 2007, 06:51 PM:

2, Not saying you're wrong, but if a componentwise imaging artifact, why does it only appear at that one point? It also looks like a continous spectrum rather than three components to me.

#6 ::: Serge ::: (view all by) ::: October 22, 2007, 07:15 PM:

James Bond will be back in Cassini Royale...

#7 ::: Serge ::: (view all by) ::: October 22, 2007, 07:26 PM:

Abi @ 3... And she sings this to her dog, TauTau Ceti...

#8 ::: Paul Duncanson ::: (view all by) ::: October 22, 2007, 07:28 PM:

Hamilton Lovecraft @ 5 That issue is addresed at Phil Plait's page on the images. The bright spot is wider than the movement between component frames and the overlapping areas blend to give the spectrum.

#9 ::: Joel Polowin ::: (view all by) ::: October 22, 2007, 07:31 PM:

Lovecraft @ 5: The colour-spread effect seems to be fairly closely aligned with the lines of the rings, so it wouldn't tend to affect them much. The planet is less well resolved and dimmer, so again, the effect wouldn't be so obvious.

As for the apparent continuous spectrum... just guessing here, but if you had a bell-like brightness distribution in a white source, and superimposed the red, green, and blue images with an offset, I think that the combinations of colours would produce that appearance.


/\ /\ /\
/B \/G \/R \
/ /\ /\ \
/ / \/ \ \
B G Y O R

#10 ::: Joel Polowin ::: (view all by) ::: October 22, 2007, 07:34 PM:

Hmm, that didn't work so well. (I accidentally hit the "Post" button instead of the "Preview" button... after several unsuccessful attempt to find a tag that would force a monospaced font. Any suggestions?)

#11 ::: Peter Erwin ::: (view all by) ::: October 22, 2007, 07:37 PM:

2, Not saying you're wrong, but if a componentwise imaging artifact, why does it only appear at that one point? It also looks like a continous spectrum rather than three components to me.

"only ... at that one point": because that's the back-scattered light of the Sun, which forms a localized bright spot. The rest of the rings (and Saturn itself) are almost continuous, so their colors stay the same when the individual (filtered) exposures are slightly shifted.

"continuous spectrum": as Phil Plait points out, it's an effect of the blend, because the three "primary-color" components (from the individual filtered exposures) are large enough and close enough to overlap, and because they were taken in a sequence of red-green-blue (or blue-green-red).

(Besides, Phil Plait is just passing on what the Cassini imaging group says about it; I'd figure they know what they're talking about...)

(Also pretty cool: a movie showing the tiny moon Prometheus colliding with the outer F ring.)

#12 ::: John Houghton ::: (view all by) ::: October 22, 2007, 09:08 PM:

<pre>


///|||\\\
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</pre>

It does add some extra whitespace around the preformatted text.


#13 ::: P J Evans ::: (view all by) ::: October 22, 2007, 09:38 PM:

I went to the Cassini site and watched one of the movies of the spot moving across the rings. No color, though.

(It may not be a really humongous diffraction grating, but the effect sure looks like it is.)

#14 ::: Rob Rusick ::: (view all by) ::: October 22, 2007, 09:59 PM:

First saw it as a star or planet shining through the rings... then realized it couldn't be shining through the planet Saturn.*

Figured it could be a reflection of the sun (which apparently it was, by #11).


* SF geekness: saw something wrong in the opening credits of Star Trek TNG 2nd Season, but couldn't figure out what it was. It was several weeks before I realized that when they panned away from the ringed planet to the Enterprise, the starfield seen through the rings didn't match the starfield the starship sat in.

#15 ::: Joel Polowin ::: (view all by) ::: October 22, 2007, 10:00 PM:

Thank you.

   /\  /\  /\
/B \/G \/R \
/ /\ /\ \
/ / \/ \ \
B G Y O R
is what I was trying to show.

#16 ::: Matt McIrvin ::: (view all by) ::: October 23, 2007, 12:16 AM:

Registration problems leading to rainbow fringes are common in color composites from Cassini photos, because the spacecraft and the target are often moving significantly between color channels.

One interesting thing I (probably re-) discovered while I was messing around with JPEGs off the raw image site with a photo editor is that if your misregistration problem produces red and blue fringes, it's much less noticeable than if you create, say, green and magenta or yellow and cyan fringes. Part of this is just that the eye is less sensitive to red and blue light than to green, but I'm guessing (just guessing) that part of it is that our heads do a certain amount of inherent correction for chromatic aberration in the eyeball.

#17 ::: Merav ::: (view all by) ::: October 23, 2007, 12:34 AM:

Joel? You make the world better through sheer geekiness. Just saying'.

#18 ::: Niall McAuley ::: (view all by) ::: October 23, 2007, 04:53 AM:

In Saturn's Rings. The Clouds of Saturn. Beyond the Rings of Saturn. The Cassini Division.

#19 ::: Teresa Nielsen Hayden ::: (view all by) ::: October 23, 2007, 11:57 AM:

Just sayin', I love being here.

#20 ::: Xopher ::: (view all by) ::: October 23, 2007, 12:10 PM:

TNH 19: And so do we. Thank you for having us in your house. *bows*

#21 ::: OtterB ::: (view all by) ::: October 23, 2007, 12:13 PM:

abi @3 *applause*

I'm singing in the rings
Just singing in the rings...

#22 ::: Martin Schafer ::: (view all by) ::: October 23, 2007, 12:23 PM:

There is a short talk by Carolyn Porco on the Cassinni mission recently posted to ted.com. If you haven't been to the site I'd strongly recommend it. A vast array of short smart talks on fascinating subjects.

#23 ::: Keith ::: (view all by) ::: October 23, 2007, 05:10 PM:

I'm constantly amazed by the images we receive back from our space probes and telescopes. To see images like this and think, "that thing right there, is a million miles away and I'm looking at it with my own two eyeballs (with help from a really bitchin' pair of specs, of course)!"

If this isn't nice I don't know what is.

#24 ::: Bruce Cohen (SpeakerToManagers) ::: (view all by) ::: October 23, 2007, 05:23 PM:

Remember the first Voyager encounter with Saturn, when we all knew we were going to see marvelous things, and had no idea what they would be? When there were science fiction writers crawling out of the woodwork at JPL to see the pictures as they came in? When astronomers were completely flabbergasted, gobsmacked, and dumfounded by braided rings and shephard moons?

It's still like that. We still keep seeing new and amazing things. The universe has an unending ability to surprise and astonish us. Thanks, universe!

#25 ::: Steve C. ::: (view all by) ::: October 23, 2007, 05:24 PM:

Keith #23

Yes, indeed. It's been an amazing 48 years (it was 1959 when Luna 3 returned the first pictures from the back side of the moon).

I remember staying up very late when Surveyor 1 soft landed on the moon and seeing those first images.

And then the Pioneer probes with those spectacular images of Jupiter and Saturn.

Wonderful stuff!

#26 ::: Emma ::: (view all by) ::: October 23, 2007, 05:51 PM:

I remember being woken up by my father one night and creeping over to the tv set which was turned away from its usual position -- and the nearest window was closed, which was unusual -- and watching a grainy little black and white picture of a man jumping off a ladder. My dad told me that the Americans had landed on the moon. And I thought how wonderful it was to be going to a country that could do such things.

#27 ::: P J Evans ::: (view all by) ::: October 23, 2007, 05:57 PM:

We were living in the Bay Area when the Pioneers went by Jupiter. The local cable company got a feed straight from NASA-Ames, before the images were processed. We literally watched the pictures coming in. (That was right after we got a color TV.)

#28 ::: C. Wingate ::: (view all by) ::: October 23, 2007, 06:04 PM:

I've been blessed with a second-row seat, as it were: my father helped design a lot of those things.

#29 ::: Tina B ::: (view all by) ::: October 23, 2007, 06:10 PM:

I put it on my desktop. Astronomical pics are the ones I like best for the computer at rest.

#30 ::: Xopher ::: (view all by) ::: October 23, 2007, 06:11 PM:

Bruce 24: We still keep seeing new and amazing things. The universe has an unending ability to surprise and astonish us. Thanks, universe!

This is why I cannot understand why anyone needs anything more than the universe itself to worship, or how anyone, especially someone who IS aware of the awe-inspiring majesty of the universe, can have any attitude toward it OTHER than worship.

I mean, people have explained it to me. I get it intellectually. I just cannot grok it at all.

#31 ::: Steve C. ::: (view all by) ::: October 23, 2007, 06:27 PM:

Xopher #30 -

It's Too Big for a lot of people. We want our Infinitely Powerful and All-Seeing deities to be conveniently packaged in the Father-sized containers.

#32 ::: Xopher ::: (view all by) ::: October 23, 2007, 06:57 PM:

Steve 31: That's what metaphors are for. Or meta-for.

#33 ::: ema nymtonsti ::: (view all by) ::: October 23, 2007, 07:17 PM:

I'm nodding enthusiastically at so many comments: I like astronomical background images too (my current one is this one of the southern cross from APOD); and when asked about my religious feelings start babbling incoherently about the universe and the massive, magestic sweep and cycle of everything in it.

Voyager fans might like to listen to Matt Howden's Voyager project. Choose "voyager" in the little drop down menu, and you'll find a small sample. I ordered the CD on the basis of the sample, and wasn't disappointed. Matt also packages things wonderfully. And there are cellos!

#34 ::: Joel Polowin ::: (view all by) ::: October 23, 2007, 07:27 PM:

Merav @ 17: It's not entirely the way I'd prefer to be making the world a better place, but I'll take it. Thanks for saying so.

#35 ::: Bruce Cohen (SpeakerToManagers) ::: (view all by) ::: October 23, 2007, 08:46 PM:

We look beyond the world's air,
to find the universe' surprise;
for joys like these we can't prepare.

The telescope extends our stare,
the jewels of worlds in our eyes.
We look beyond the world's air.

With radio we try to share
music to which the spheres give rise
For joys like these we can't prepare.

Our probes take years to go out where
all we have is wild surmise.
We look beyond the world's air.

To look far out beyond the glare,
to look at distant alien skies,
for joys like these we can't prepare.

Now we hope to take the dare,
to go ourselves and see the prize.
We look beyond the world's air,
For joys like these we can't prepare.

#36 ::: Tina B ::: (view all by) ::: October 24, 2007, 02:39 AM:

#33 ema -- was just telling someone that when Professor Gunn had a student from Argentina, I took her out at night and showed her the Big Dipper. If I went there I'd have to go out and see the Southern Cross myself.

#37 ::: ema nymtonsti ::: (view all by) ::: October 24, 2007, 06:22 AM:

#36 Tina: What's lovelier and more humbling than the night sky? One of the most amazing things when I left the city for a small town in the mountains was how many millions degrees of better the night sky suddenly became. Back in the city I could see really big night sky things like planets and eclipses, but here the sky is thickly iced with the Milky Way and more stars than you can count, and more appearing the longer you look. My new favourite constellation is the pleiades, but of course I'm loyal to the southern cross :) Wouldn't it be lovely if you could really *see* those colours?

#38 ::: Fragano Ledgister ::: (view all by) ::: October 24, 2007, 07:28 AM:

Bruce Cohen (SpeakerToManagers) #35: Nice!

#39 ::: John Houghton ::: (view all by) ::: October 24, 2007, 09:21 AM:

emma (26):
Out of curiosity, where did you grow up that you had to hide the fact that you were looking at the moon landing on TV?

#40 ::: Tim Kyger ::: (view all by) ::: October 24, 2007, 09:37 AM:

Just now getting a chance to see Making Light again after, oh, um, life.

Yes, I *know* it ain't a diffraction effect. That was a nerdly joke. Just like the one about the weather in Houston.

"Hey, ya know, Houston? Yeah, the air there is at the triple point of water."

Shaaa-boom.

I'm here 'til Thursday. Thank you, you've been a lovely crowd.

#41 ::: Jakob ::: (view all by) ::: October 24, 2007, 09:53 AM:

Tim Kyger: not being a native, I can't comment, but I'd always thought of Houston as hot and humid; 273K seems a little... cold for my mental image.

#42 ::: Emma ::: (view all by) ::: October 24, 2007, 10:06 AM:

John@39: Cuba. It was jail time if they caught watching American TV (they couldn't block the Miami stations in those days), so , of course, everybody watched it.

#43 ::: Joel Polowin ::: (view all by) ::: October 24, 2007, 10:07 AM:

Critical point, maybe? Where liquid and gas become indistinguishable? For water, that's 647 K (374 °C) and 218 atm. pressure.)

#44 ::: Bruce Cohen (SpeakerToManagers) ::: (view all by) ::: October 24, 2007, 11:58 AM:

Fragano Ledgister @ 38

Thank you. It's hard not to be inspired by those rings.

#45 ::: C. Wingate ::: (view all by) ::: October 24, 2007, 02:06 PM:

BTW, here's a way to see the glory without buying a plane ticket and hoping you get lucky: what you need is a reflectorized highway sign ("DO NOT ENTER" seems to work best) positioned so that a floodlight will throw your shadow on the sign. Station yourself so that the shadow of your head covers about half the width of the sign, and you should see the glory surrounding the shadow.

#46 ::: Rob Rusick ::: (view all by) ::: October 24, 2007, 03:17 PM:

Re: #45: Nowdays, when they put down white striping at the crosswalks, they dust the striping with glass beads that will increase their reflectivity. These beads get spread all over the road surface, and collects in the hollows. With a high sun behind me, I've frequently seen a glory surrounding my shadow on the road surface.

They throw enough of this glass bead material around that it will collect at the curbs. I'd collected a good-sized jar's worth, going out to the street with a dustpan and a whiskbroom (I planned to use the material in some art project I never got around to doing).

#47 ::: Joel Polowin ::: (view all by) ::: October 24, 2007, 03:18 PM:

C. Wingate @ 45: I suspect that effect may be heiligenschein rather than a glory. The former is a diffraction effect and produces rainbow rings; the latter is purely a reflective effect. (I was seeing heiligenschein around this time last year, cycling home at oh-god-o'clock times and seeing my shadow from street lights on dewy grass, with the shadow of my head showing a halo.)

#48 ::: C. Wingate ::: (view all by) ::: October 24, 2007, 03:32 PM:

re 47: Actually they have the same cause (backscattered light towards the source). The difference is that the glory occurs when the backscattering comes from spherical "sources" of uniform size, such as might be found in a cloud or fog bank or sign with glass beads. The defraction creates the rings of color; in heilegenschein the "reflectors" lack this uniformity and thus blur the colors together. In the cases I've seen the signs produce exactly the same pattern of iridescent color seen in the pilot's glory.

#49 ::: P J Evans ::: (view all by) ::: October 24, 2007, 03:34 PM:

Rob @ 46

My father had some sub-millimeter glass beads (like the ones they put on paint).
The bag had an expiration date on it.
I never figured out how glass beads would expire.

#51 ::: Joel Polowin ::: (view all by) ::: October 24, 2007, 08:13 PM:

C. Wingate @ 48: Ah, okay. I hadn't thought that one could obtain the same effect from a 2-dimensional sheet of reflectors, but now that I think about it, it makes sense.

#52 ::: Rob Rusick ::: (view all by) ::: October 24, 2007, 08:58 PM:

P J Evans @49: I never figured out how glass beads would expire.

I wouldn't have thought that it could, either. It's probably as fresh to eat old as new.

Could fine glass beads 'cake' together (becoming harder to shake out of the bag)?

Would they melt at all (becoming less spherical and degrading the reflection)?

If they expire, wouldn't it mean they wouldn't be effective in your application after the time elapsed (the highway sign timed out).

It struck me too that maybe this could (not likely) describe 'rights management' (my license for the glass beads expired).

#53 ::: Marilee ::: (view all by) ::: October 24, 2007, 09:10 PM:

P J Evans, #49, it's not the beads that expire, but the bag they're in. They can't be guaranteed without contaminant after that period, so probably are not as useful for the proposed purpose.

A lot of things that have expiration dates don't mean the content, but that the content won't be sterile after that date because the container will start to break down. Ever noticed the expiration date on bottles of water? The water doesn't suddenly get bad; the plastic starts leaching into the water.

#54 ::: C. Wingate ::: (view all by) ::: October 24, 2007, 09:29 PM:

re 51: The curious thing is that the 2-D sign vs. the 3-D cloud doesn't affect the appearance of the glory as having depth. It's the slight difference in perspective of the two eyes that does it.

#55 ::: Rob Rusick ::: (view all by) ::: October 24, 2007, 09:54 PM:

Marilee @53: Good point and well illustrated.

#57 ::: P J Evans ::: (view all by) ::: October 25, 2007, 10:42 AM:

Marilee @ 53

Ah. Although in that case (those cases?) the label really should say that it's the container that expires.

#58 ::: Bill Higgins-- Beam Jockey ::: (view all by) ::: October 25, 2007, 11:49 AM:

Speaking of astronomy, yesterday I learned that a dim comet has suddenly become 400,000 times brighter. Once again, The Bad Astronomer is on top of it.

It's a naked-eye object now, third magnitude. And it should evolve interestingly, as we watch.

Was cloudy last night over Aurora, but I plan to check this out as soon as Comet Holmes is visible in my sky!

#59 ::: Steve C. ::: (view all by) ::: October 25, 2007, 12:31 PM:

Bill #58 -

Thanks for the heads up on Holmes. I'll be checking it out tonight.

#60 ::: ethan ::: (view all by) ::: October 25, 2007, 03:55 PM:

I don't see anywhere an explanation for why the comet would suddenly go all bright. Is it aliens?

#61 ::: abi ::: (view all by) ::: October 25, 2007, 04:00 PM:

I, for one, welcome our new ice overlords.

#62 ::: Steve C. ::: (view all by) ::: October 25, 2007, 04:22 PM:

Ethan, comets can brighten quite suddenly as volatile pockets of dust and ice erupt. An event of this magnitude is rare, however.

#63 ::: Paul Duncanson ::: (view all by) ::: October 25, 2007, 07:48 PM:

Best guess is that it's a weather balloon reflecting Venus onto some swamp gas. Nothing to see here.

Either that or it's a larger than usual outgassing or the thing is breaking up.

It seems Comet Holmes has a history of suddenly brightening. It did it back in 1892.

#64 ::: Faren Miller ::: (view all by) ::: October 26, 2007, 11:23 AM:

The latest Astronomy Picture of the Day shows the comet, with a US photo rather oddly inset into a night street scene in Tehran.

(I tried to give the link properly, but Comments keeps deleting the closer at the end, so you'll have to go here: http://antwrp.gsfc.nasa.gov/apod/ap071026.html)

#65 ::: Rob Rusick ::: (view all by) ::: October 26, 2007, 08:02 PM:

abi @61: You know who else did? Hitler...

#66 ::: David Goldfarb ::: (view all by) ::: October 27, 2007, 06:37 AM:

Last night when I first read about the comet, it was very cloudy here. Tonight in the evening there were thin clouds, but I was able to see the comet with the aid of binoculars -- it was definitely the comet, a fuzzy ball where the stars were points of light. This is only the third comet I've ever seen, although it's rather less impressive than Hyakutake or Hale-Bopp were.

#67 ::: Niall McAuley ::: (view all by) ::: October 27, 2007, 12:34 PM:

It's not just naked eye visible, last night I was able to get a photo of it, with a very ordinary little camera.

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