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A member of a broad category of stars that have luminosities between 10 and 1,000 times that of the Sun, and radii typically between 10 and 100 times the Sun's. A star becomes a giant when the hydrogen fuel available for nuclear fusion reactions in its core is depleted and the adjustment to the new energy balance causes the outer layers to expand greatly. The surface temperature drops, but the total luminosity rises because of the great increase in surface area. Examples are Capella, Aldebaran and Arcturus. Massive hot stars, which are very large in comparison with the Sun even before they reach a late stage of evolution, are sometimes also referred to as giants. See also: Hertzsprung-Russell diagram, red giant, stellar evolution. |