Fingerprints in the Light This graph, or spectrum, shows the
light from a dusty, distant galaxy located 11 billion light-
years away. The galaxy is invisible to optical telescopes, but
NASA's Spitzer Space Telescope was able to capture the light
from it and dozens of other similar galaxies using heat-seeking
infrared eyes. Spectra are created when an instrument called a
spectrograph spreads light out into its basic parts, like a
prism turning sunlight into a rainbow. They contain the
signatures, or "fingerprints," of molecules that contribute to
an object's light. In this case, the galaxy's spectrum reveals
the fingerprint for silicate dust (large dip at right), a
planetary building block like sand, only smaller. This
particular fingerprint is important because it helped
astronomers determine how far away the galaxy lies, or more
specifically, how much the galaxy's light had stretched, or
"redshifted," during its journey to Spitzer's eyes. Because the
universe is expanding, a galaxy's light will shift toward r