Moon Illusion tricks the eye

Jan 19, 2011 By Nancy Atkinson
Enceladus and Dione, as seen by Cassini. Credit: NASA/JPL/Space Science Institute

We’ve all experienced the Moon Illusion, where our own full Moon looks bigger when seen on the Earth’s horizon. But how about this illusion where you can’t really tell which of these two moons of Saturn is actually bigger, or which is closer, as seen by the Cassini spacecraft? Here, Dione, top right, appears closer to the spacecraft because it is larger than the moon Enceladus, lower left. However, Enceladus was actually closer to Cassini when its visible light, narrow-angle camera took this image.

Dione (1,123 kilometers, or 698 miles, across) is more than twice the size of Enceladus (504 kilometers, or 313 miles, across). The two moons are contrasted with Enceladus’ bright, reflective trailing hemisphere, and Dione’s darker, micrometeor-dusted side, decorated with wispy lighter materials.

Cassini took this image on Dec. 1, 2010 from about 510,000 kilometers (317,000 miles) from Enceladus and approximately 830,000 kilometers (516,000 miles) from Dione. Image scale is 3 kilometers (2 miles) per pixel on Enceladus and 5 kilometers (3 miles) per pixel on Dione.

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More information: www.ciclops.org/view/6661/Diones_Deception?js=1

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User comments : 6

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geokstr
2.8 / 5 (6) Jan 19, 2011
Wow!

What an amazing scientific insight! Who woulda ever thought it!

Something will look bigger if it's closer! It might even look bigger than something that's actually bigger but farther away, even though it's really smaller.

I'm flabbergasted, just blown away, by this wondrous finding.

Gosh, I sure hope they took lots of telescope time and grant money coming up with this conclusion. Otherwise we'd just have wasted it on real science and stuff.

You can't make this stuff up.
TheTim
5 / 5 (1) Jan 19, 2011
Umm..I'm not sure I get it...

I thought the moon at lower left was closer...Guess the "illusion" didn't work on me...
Blakut
3.6 / 5 (5) Jan 19, 2011
@geokstr it's an image from space, not from a telescope on earth. And the purpose was not to show you that objects that are far away look smaller. It's just what this article right here says...
geokstr
3.4 / 5 (5) Jan 19, 2011
Blakut:

And the camera on Cassini doesn't use a telescopic lens, and there aren't competing claims on the use of that camera? Please, this whole article is ridiculous.

Look, a picture and stuff! Cool, hey! Let's write something that sounds neat!
sstritt
3 / 5 (2) Jan 19, 2011
From The Comments Guidelines: "avoid pointless verbiage"
Should also apply to the articles.
technicalengeneering
not rated yet Jan 20, 2011
completely baffled....