The Moon's an arrant thief, and her pale fire she snatches from the Sun

By Sean Carroll | May 29, 2006 10:39 am

Well, not all of it. Some of the Moon’s pale fire is actually snatched from cosmic rays, as seen in the Astronomy Picture of the Day from last Friday.

Gamma-ray Moon
This is an image of the Moon in gamma rays, taken by NASA’s EGRET telescope. The gamma rays are produced by cosmic rays (which aren’t electromagnetic radiation at all, but mostly high-energy protons) striking the lunar surface. There is no equivalent process for the Sun, and in fact the Moon is much brighter than the Sun in gamma rays.

The Sun has some tricks of its own, of course. The Moon picture reminded me a bit of this one:

Neutrino Sun
They’re both circular false-color blobs, so I suppose the resemblance isn’t so surprising. But this is an image of the Sun in neutrinos, reconstructed using data from the Super-Kamiokande neutrino detector in Japan. (Yes, the one that was essentially destroyed in a freak accident. But it’s now back online, and meanwhile I’m sure Koshiba’s Nobel Prize was some consolation.) The Sun, of course, makes its own neutrinos, but it’s amazing that we can actually image a celestial object using something other than photons!

Besides photons, cosmic rays, and neutrinos, there aren’t that many ways we get to observe the universe. I’m looking forward to the first images of either the Sun or Moon in gravitational waves.

Update: As Alex R. mentions in the comments, Ray Davis passed away on Wednesday. He was the pioneer in solar-neutrino measurments, overseeing the Homestake mine experiment, and shared the Nobel with Koshiba.


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Cosmic Variance

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About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] .


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