Branch of astronomy concerned mainly with the properties and structures of cosmic objects, including the universe as a whole. Starting in the 19th century, spectroscopy and photography were applied to astronomical research, making it possible to study the brightness, temperature, and chemical composition of cosmic objects. It was soon realized that the properties of these bodies could be fully understood only in terms of the physics of their atmospheres and interiors. X-ray astronomy, gamma-ray astronomy, infrared astronomy, ultraviolet astronomy, and radio and radar astronomy are all basically concerned with extending electromagnetic coverage beyond the visible spectrum to constrain the physical characteristics of astronomical objects.

This entry comes from Encyclopædia Britannica Concise.
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