"JG" == Jim Greenfield writes:

[Regarding high-energy cosmic rays, the Auger Observatory, and
cosmic-ray air showers:]

However, Matthews says, there are two dependable ways to detect
them. Each makes use of the fact that, when a high-energy cosmic
ray strikes the earth's atmosphere, it blasts apart into a shower
of particles that fall to the ground, primarily in the form of
electrons.

First, it is possible to observe the shower that develops in the
atmosphere when the rays hit. Matthews says that the shower
produces a weak fluorescence -- "a line of faintly glowing
atmosphere" -- that can be observed with the special "Fly's-Eye"
fluorescence telescopes that observe the sky in all directions.
Second, it is possible to collect or detect the falling particles
using water-tank detectors widely dispersed on the ground.

JG If the time it takes these "lines of fluorescence" to be produced,
JG and their length known, can the velocity of the particles be
JG established? (uh ho!!! faster than "c" !!!!!!!!!!)

I think that these things can be measured. You won't like the answer,
though. Cosmic rays, and the particles produced in an air shower, are
one of the classical demonstrations of special relativity.
Specifically, muons produced in the CR air showers should not reach
the ground based on their rest lifetimes and the distances above
ground at which they are produced.

If one takes relativistic time dilation into account, however, there's
no problem.

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