Astronomy often gets lumped with physics when universities decide how to compartmentalize human knowledge and allocate office space. There's some sense to this: after all, most astronomers are pretty good at physics, and the pros, at least, have to use physics on a daily basis.
But in other ways it's misleading. Physicists can touch the objects of their study, rolling them down inclined planes, energizing them with microwaves, or charging them up with static electricity. When's the last time you touched a star?
Actually, you can. Or, rather, the stars can touch you. Microscopic bits of star-stuff are constantly zooming through space. They're called cosmic rays - somewhat misleadingly, it turns out, for they are tiny chunks of subatomic matter. Usually they are the nuclei of atoms (the cores, around which electrons whirl in chemistry textbooks and old sci-fi movies); occasionally they're something more exotic. They cruise the galaxy at many millions of miles per hour.
Most cosmic rays go nowhere near Earth. But when some of these subatomic fastballs slam into Earth's atmosphere, they light up the night sky ever so slightly - just enough to be seen by super-sensitive electronic eyes in remote parts of Utah and Argentina.
Recent research suggests that most cosmic rays are the debris of supernovae - cataclysmic explosions that bring the lives of the biggest, brightest stars to an abrupt end. A few of these bits of stellar shrapnel pass through your body every day. Many more do so when you fly above a third of the Earth's atmosphere in a passenger jet.
Cosmic rays can teach us a lot about certain chapters in the life stories of stars. So can neutrinos, even-tinier particles that astronomers catch in underground mines or Antarctic ice. But nearly everything we know about the stars comes from studying light. And that makes astronomy, in one sense, a voyeuristic science. We can't roll the stars down inclined planes or rub them with rabbit fur. Rather, like Chauncey Gardiner, the TV-addicted protagonist of Jerzy Kosinsky's novel Being There, we astronomers "like to watch" - indeed, we have no other choice.
What's more, light takes time - lots of time - to reach us after leaving a star's blazing outer atmosphere. Sunlight takes about 8 minutes to reach us from our home star. And light from Alpha Centauri - the nearest of the night sky's bright stars - takes more than four years to reach Earth. Look at M31, the nearest spiral galaxy to our own star-city, the Milky Way, and you'll see light that has traveled two and a half million years to tickle our retinas.
The fact that light takes time to go from point A to point B is something that Albert Einstein made famous in his special theory of relativity. It makes the light we gather from the stars into cosmic fossils, relics from the past. Like fossils, the older the light is, the harder it usually is to find and study. Consequently, we astronomers have a rather fuzzy view of the universe's early epochs and a relatively sharp impression of its recent past - not unlike geologists, with their abundant dinosaur fossils but ultra-rare Precambrian ones.
As for touching the stars, those who have limited vision, or none, can learn rich astronomy lessons from the numerous delightful books that award-winning author Noreen Grice has lovingly written and illustrated over the years. Noreen's books bring high-tech astronomy, lunar phases, and the Sun and stars to life with Braille lettering and tactile illustrations. You don't have to have limited vision to enjoy these books and learn from them.
P.S. Click here for an extremely cool comic book (in PDF format) on cosmic rays from Nagoya University in Japan.
Copyright 2009 Joshua Roth.