Direct images are used by astronomers to locate heavenly objects spatially, understand their structure, determine their brightness, and study their motions across the line of sight. The second way astronomers use light from celestial objects is to spread it into its constituent rainbow colors, or wavelengths. This is called spectroscopy, and spectroscopic observations are used to determine temperatures and chemical abundances of objects, as well as to find their speed toward or away from us. Both types of observations are made at Lick Observatory.
Infrared observations look at colors, or wavelengths, beyond the range of human vision.
For these wavelengths, the natural sky brightness is much greater than man-made sources, even near large cities. In high-resolution spectroscopy, light from a star is spread out so much in color that only fairly bright stars can be observed, and sky brightness is not a problem. Studies of this kind led to the discoveries of extra-solar planets. AO allows astronomers to obtain highly detailed images of small regions. Such images are usually recorded in the infrared and so are not affected by artificial lights.