Gamma-ray Moon

[Martin]

Strange that the moon is brighter than the sun, at gamma-ray wavelengths.

 

http://antwrp.gsfc.nasa.gov/apod/ap060527.html

 

which is today's Astronomy Picture of the Day (May 27, 2006).

 

This is not really NEWS news, but it's strange the moon glows more brightly.

 

Earth's atmosphere blocks gamma---otherwise, if you had gamma-ray eyes, the moon would be blazing away in the sky but the sun might be so dim as to be invisible.

 

Anybody want to say why that is?

[Psycho]

It says below why it is.

 

So why is the Moon bright? High energy charged particles, known as cosmic rays, constantly bombard the unprotected lunar surface generating gamma-ray photons.

[Martin]

High energy charged particles, known as cosmic rays, constantly bombard the unprotected lunar surface generating gamma-ray photons.

 

Thanks, and why doesnt the same thing make the sun's surface glow in the gamma wavelengths just like the moon's? What is different about it?

 

(you may know, or have a guess, which would be great. if not, we get somebody else to tell us)

[reor]

I'd guess it's the difference of the surfaces.

[Martin]

I'd guess it's the difference of the surfaces.

 

Good guess. one nice thing about the SFN format is you CAN guess, and you may get someone who knows (like Swansont) to say if the guess is right or not.

 

I will hazard a guess that the sun's ATMOSPHERE SCATTERS gammaray photons.

 

so if a cosmic ray DID happen to come in and hit an atom near the sun's surface in such a way that a gamma photon was produced, then that gamma photon would not have the chance of a snowball in Hell of getting clear of the sun

 

because as it tried to go anywhere it would constantly be colliding with other stuff---getting scattered again and again and gradually losing energy as it was getting absorbed and re-emitted----until it finally had dwindled down to be a bunch of mediocre photons: no longer worthy of the proud name of gamma.

 

scattering a gamma photon is like breaking a $100 bill. If you keep doing equal random trades you eventually most likely wind up with small change.

 

the cool thing about the moon------I am guessing-----is that it has pure vacuum. As soon as that gammaray is produced (by a cosmic ray reaction) it has nearly perfect vacuum to fly off into. so it escapes from the dismal prospect of repeated scattering

[reor]

How do gamma rays react on magnetism?

[MattC]

Gamma rays are just high energy light. Light, as far as I know, is not influenced by magnetic fields.

That almost seems odd to me, since light is a wave in the electric and magnetic fields, but I have never heard of light being influenced by magnetism. I expect that the magnetic field would be a sum (at a given point) of the magnetic fields of light waves and other magnetic fields, but that the two would not really affect each other - that is, the light would pass through a magnetic field, and the magnetic field, if we measured it, would be disturbed by the magnetic portion of light, but when the light left the field it would be unchanged and the magnetic field (and the object that generates it) would likewise be unaffected.

 

Hopefully some experts can confirm/clarify these comments.

[olifhar]

Good guess. one nice thing about the SFN format is you CAN guess' date=' and you may get someone who knows (like Swansont) to say if the guess is right or not.

 

I will hazard a guess that the sun's ATMOSPHERE SCATTERS gammaray photons.

 

so if a cosmic ray DID happen to come in and hit an atom near the sun's surface in such a way that a gamma photon was produced, then that gamma photon would not have the chance of a snowball in Hell of getting clear of the sun

 

because as it tried to go anywhere it would constantly be colliding with other stuff---getting scattered again and again and gradually losing energy as it was getting absorbed and re-emitted----until it finally had dwindled down to be a bunch of mediocre photons: no longer worthy of the proud name of gamma.

 

scattering a gamma photon is like breaking a $100 bill. If you keep doing equal random trades you eventually most likely wind up with small change.

 

the cool thing about the moon------I am guessing-----is that it has pure vacuum. As soon as that gammaray is produced (by a cosmic ray reaction) it has nearly perfect vacuum to fly off into. so it escapes from the dismal prospect of repeated scattering[/quote']

 

It would make sense that the sun's outer atmosphere scatters/absorbs gamma rays in a way somwhat similar to the atmosphere of the earth... stuff gets ionized, electrons get ejected, or compton scattering occurs etc. I don't really know much about that, so I may be terrifyingly wrong.

 

I know cosmic rays have been observed at energy levels up to 10^20 eV, but what would be considered "usual" for those things? Surely most are in the range for Compton scattering, but I'm just wondering.

[Martin]

It would make sense that the sun's outer atmosphere scatters/absorbs gamma rays in a way somwhat similar to the atmosphere of the earth... stuff gets ionized' date=' electrons get ejected, or compton scattering occurs etc. I don't really know much about that, so I may be terrifyingly wrong.

 

I know cosmic rays have been observed at energy levels up to 10^20 eV, but what would be considered "usual" for those things? Surely most are in the range for Compton scattering, but I'm just wondering.[/quote']

 

instead of being wrong, I say you are RIGHT! (unless Swansont or Atheist or others come in and contradict, which they have not so far)

 

and also, you dont have to worry about the top energy of cosmic ray because that does not get all converted into one humongous gamma photon. the cosmic ray makes a little explosion or "shower" of pieces like a glass shattering into many pieces. so the actual gammaray photons that result have more reasonable energies that one could imagine being dwindled away by the reactions that you mention

 

thanks for considering the details!

 

You have a very nice quote from Geoffrey Chaucer rendering the Latin saying "ars longa, vita brevis" and something written in Mordor Elvish on your personal info page. I am curious where did you pick up all the Liberal Arts stuff, or is this just normal for computer guys.

[olifhar]

instead of being wrong' date=' I say you are RIGHT! (unless

You have a very nice quote from Geoffrey Chaucer rendering the Latin saying "ars longa, vita brevis" and something written in Mordor Elvish on your personal info page. I am curious where did you pick up all the Liberal Arts stuff, or is this just normal for computer guys.[/quote']

 

The short explanation is that I've always been interested in many things, probably too many things at once. So Chaucer's rendering of the Latin is particularly interesting for me-- so many things to learn, not enough time to master even most of them.

 

Tolkien's fiction, world, scripts and languages were an integral part of my childhood, and also kindled my interest in literature and languages. I studied Latin in secondary school and really enjoyed it, was considering concentrating in classics when I went to university, but alas, it was one of many things were calling to me, and I had to choose between them for the time being.

 

As for the normal part, I can't say for sure, but I highly doubt I'm anything of the sort.