The ups and downs of Saturn pictures

By Phil Plait | June 11, 2012 1:00 pm

When I look at Cassini images of Saturn — with its multitude of rings and fleet of moons — I am inspired, moved, and even awed.

And sometimes I laugh. When I saw this image, for example, I actually chuckled to myself. Why?

[Click to encronosenate.]

This gorgeous shot was taken on December 30, 2011 and released just today as the Cassini Image of the Week. It shows Saturn’s gorgeous rings seen nearly edge on, and the tiny moon Epimetheus, only 113 kilometers in diameter, next to them.

It’s a lovely image to be sure, and my very first thought was; I wonder if Epimetheus is closer to us than the rings, or farther away? If we’re looking down on the rings, from the north, then Epimetheus is closer to us. But if we’re looking up from underneath the rings, Epimetheus is on the other side of the rings. I could mentally switch my perspective back and forth, but I couldn’t tell which view is correct! This prompted my chuckle, as I wryly smiled at my brain’s confusion (I love optical illusions).

So take another look: are we looking down on the rings, or up? Hint: the Sun is shining from the north, down on the rings.

It’s a bit of a conundrum, isn’t it? Just by looking it’s almost impossible to figure out! If you’re familiar with Cassini pictures, the rings look subtly different if they are illuminated from above and you’re looking at them from underneath, and vice-versa. But it’s hard to tell. And to be honest, I wouldn’t have known without reading the caption for the image.

The answer is we’re looking up. The Sun is shining down on the top of the rings, and we’re looking up from underneath, putting wee Epimetheus about 1.5 million kilometers (900,000 miles) from Cassini when this picture was taken. If it helps, hold up something round like a DVD and look at it from underneath. As another helpful guide: in the image above, the part of the rings at the top of the picture are closest to you, the bottom farther away, and Epimetheus father still.

And I bet that even knowing that, some of you are having a hard time picturing it. Our brains are funny things, easily fooled when there’s symmetry in a picture, especially when that picture shows an unfamiliar object. I’m sure Carolyn Porco can just glance at something like this and figure out everything she needs to understand the geometry! I’m not so sure I could’ve.

Remember: seeing isn’t always believing. It’s easy to fool our eyes and brain, but in the end the Universe knows what it’s doing.

Image credit: NASA/JPL-Caltech/Space Science Institute


Related Posts:

- Saturn brain bender
- For moons, size does matter
- A little weekend Saturn awesomeness
- The tiny moon with the long reach

Comments (9)

  1. Carey

    To be honest, it doesn’t look “right” to me if I try to think of it as looking down on the rings (with the rings on the bottom closer to me, and the top farther away).

    In fact, this is how I initially interpreted it, but that made the outermost grouping look warped out of plane with the rest of the rings, at the top part of the picture. I thought there was something strange going on, maybe with shadows on Saturn’s surface or something.

    But when I told my brain to think about looking up at the rings, with the top rings closest to me, and the bottom rings farther away, it looked much better. You can see that there’s a much bigger gap on the top than on the bottom, between the outer group and the next, fainter, group in. Naturally, that gap would be bigger if it was closer to you, so the top must be closer.

    In fact, there are several analogous features that are bigger on top than they are at the bottom. And you don’t even have to encronosenate the picture to see them! Shouldn’t it be “enchronosenate”? Or is there another spelling of Chronos I’m unfamiliar with?

  2. Chris A.

    @Carey (#1):
    “Chronos” != “Cronus” Two different mythical beings; only the latter is a cognomen for Saturn.

  3. John S.

    I guessed we were beneath the ring plane based on two things: The F Ring seems thinner where it crosses the photo lower down; and the lower edge of the rings is less bright than the upper edge, which to my eyes says distance. Neither thing may be a reliable indicator though– I had a 50% chance of being right with just a guess.

  4. CR

    Woo-hoo!
    I got it right (looking up, not down).

  5. What I noticed was the absence of the Cassini division. I thought it was because the image was in UV light or something, but it was the unfamiliar-from-Earth backlighting! Good one!

  6. kevbo

    This is classic Bad Astronomy (as in ‘Good” Astronomy). Nice post!

  7. alfaniner

    I find that if I think of it as “Death Star approaching Yavin” it’s a lot easier.

  8. It’s a lovely image to be sure, and my very first thought was; I wonder if Epimetheus is closer to us than the rings, or farther away? If we’re looking down on the rings, from the north, then Epimetheus is closer to us. But if we’re looking up from underneath the rings, Epimetheus is on the other side of the rings.

    At first I thought that that might not necessarily follow. After all, what if Epimetheus’ orbit were inclined to the plane of the rings? Depending on the point in its orbit when the image is captured, it might then appear “up” or “down” regardless of its distance.
    Of course, then I wiki-ed Epimetheus and found that it has an extremely low inclination. So I learned something today :D

  9. I have the same problem whenever I look at a photo of craters.

    Most of the time, my mind renders the picture in my head as circular dome-shaped bumps sticking OUT of the planet/moon, not circular bowl-shaped depressions sticking in.

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