# Cosmic Rays 101. Confused.

1. Jan 18, 2005

### Glenn

http://space.com/scienceastronomy/AAS_cosmic_rays_050117.html

Quote from article... "Cosmic rays are not actually rays, like light. They are instead subatomic particles, thought to be mostly protons, on of the fundamental units of matter. The highest-energy versions of them race across the universe at more than 99.9 percent of light-speed, packing in their tiny bodies more punch than a golf ball hit by a pro, explained physicist Glennys Farrar of New York University."

Now I am confused. Cosmic rays are typically shown on the electromagnetic spectrum and compared in similar terms to Gamma Rays, X-rays, visible light, and other EM frequencies.

How did things jump from photon to proton? Where exactly is the transition? Why are they still characterized in the same way?

Thanks,
Glenn

2. Jan 18, 2005

### imabug

cosmic rays can also consist of high energy gamma and x-rays, such as those from gamma ray bursters, and x-ray sources like pulsars and black holes to name a few.

the term is a generic catch-all to cover sources of radiation from outside the solar system that smack into the earth.

3. Jan 18, 2005

### Garth

Where are they shown as part of the electromagnetic spectrum?

As highly energetic particles they have as individuals a total energy that is equivalent to a photon of a certain wavelength but they are not part of that spectrum. Unlike photons they have a rest mass and therefore cannot travel at c.

Garth

[EDIT - post crossed with imabug. Of course, I was taking Glenn's question to automatically refer to those cosmic rays not identified as gamma or X-rays.]

Last edited: Jan 18, 2005
4. Jan 18, 2005

### Labguy

I have never heard of any reference to "cosmic rays" as anything but particles, not anything in the EM spectrum. Current definition can be found at:
http://encyclopedia.thefreedictionary.com/Cosmic+ray
Anyone combining the definition or grouping it with Gamma rays is using the term incorrectly.

5. Jan 18, 2005

### Glenn

Last edited by a moderator: May 1, 2017
6. Jan 18, 2005

### chroot

Staff Emeritus
Cosmic rays DO include photons of X- or gamma-radiation. They also include particles like muons, protons, and even a few iron atoms.

- Warren

7. Jan 18, 2005

### Chronos

I'm with labguy on this one. From the NASA site
http://imagine.gsfc.nasa.gov/docs/features/topics/snr_group/cr-knee.html [Broken]
The spectrum of a cosmic ray is merely particle energies expressed in terms of electron volts. You can also represent the energy of photons, like gamma rays, in electron volts.

Last edited by a moderator: May 1, 2017
8. Jan 18, 2005

### Labguy

No, they don't. Anyone using the term as such is oversimplifying or just shortcutting for a term meaning all we get hit with (EM and particles) from space.

This definition is all I have heard used by anyone other than something generic or layman's terminology in astronomy less than 101. At college, it was called "Descriptive Astronomy"; an elective course for easy credit...

Last edited by a moderator: May 1, 2017
9. Jan 18, 2005

### Labguy

Lots of quotes on those sites, and I could easily see how they could cause some confusion. All I can say is that they are more of a generic description of all things we get bombarded with. But, lumping in energetic particles with EM radiation seems just an easy way to describe various energies arriving at Earth. As Chronos said, either can be measured with electron-volt energies but that doesn't make high-velocity particles a part of the EM spectrum. See the (arrowed) EM ranges and descriptions at:
http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html

Last edited by a moderator: May 1, 2017
10. Jan 18, 2005

### Glenn

Its making sense now. Thanks!

-Glenn

11. Jan 18, 2005

### chroot

Staff Emeritus
Aye chihuahua, I concede.

- Warren

12. Jan 19, 2005

### Norman

The best paper (in my opinion) on the Galactic Cosmic Rays (GCR) spectrum is:
"Elemental and Isotopic Composition of the Galactic Cosmic Rays"
J A Simpson
Annual Review of Nuclear and Particle Science, December 1983, Vol. 33: Pages 323-382

This paper is a great overview of the GCR spectrum. It is a little dated, so it doesn't include up-to-date information on Extremely High Energy GCRs. If you aren't comfortable with technical papers, a good introductory book is "Cosmic Rays and Particle Physics" by Thomas K. Gaisser (ISBN 0521326672)
Hope that helps.
Cheers

13. Jan 20, 2005

### Nereid

Staff Emeritus
Here is a link to the Simpson paper that may help; however, I couldn't find anything on the internet that didn't require some kind of subscription (or paying )