21-CM LINE OF ATOMIC-HYDROGEN

Discovered in 1951, the 21 cm hyperfine line of atomic hydrogen has be come one of the best-studied spectral features in radioastronomy. Used to trace the distribution and velocity of atomic gas in our own and i n other galaxies, the line has made an enormous contribution to our un derstanding of galactic structure. Now, 40 years after the line's disc overy, a low-cost receiving system can be assembled from items of cons umer electronics to enable study of the line in an undergraduate labor atory.