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I hope you enjoy the program. Hello, one of the world's largest and most unusual astronomical observatories can be found

on a vast empty plane in Western Argentina.

The Pierre O'Jé Observatory covers an area larger than Luxembourg.

Instead of telescopes, it uses 1,600 massive tanks of water to look at the heavens.

The scientists who work there aren't looking for light from the

stars or even radio waves instead they're studying cosmic rays. First identified

a century ago, cosmic rays are subatomic particles which constantly bombard the Earth from space.

The discovery of high energy radiation coming from far beyond our solar system led to the

emergence of particle physics as a new scientific discipline.

Today more scientists than ever are dedicated to the study of

Cosmic Rays, but many questions remain unanswered including most importantly where they come from.

With me to discuss Cosmic Rays are Carolyn Crawford, Gresham Professor of Astronomy and a member of the

Institute of Astronomy at the University of Cambridge. Alan Watson, Emeritus Professor of Physics at the

University of Leeds, and Tim Greenshaw Professor of Physics at the University of Leeds and Tim Greenshaw Professor of Physics at the University of Liverpool.

Karen Crawford, would you be in by giving us a slightly fuller explanation of what cosmic rays are?

Well, to start with, I think it's just reiterating what you said right at the beginning,

despite the name we're not talking about rays of light, we're talking about matter, energetic

particles that are impacting the top of the Earth's atmosphere.

They're coming from all directions and outer space and some we even think are coming from outside our galaxy.

And these are pieces of atoms and in some ways there are only direct samples of matter outside

the solar system coming towards us. They're electrically charged and they're

...