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A fifth magnitude star in the southern reaches of Boötes the Herdsman, Omicron Boötis lies some seven degrees eastward of brilliant Arcturus in the sky. Like Arcturus, this is a luminous giant star, but it is some seven times farther from the Solar System than Arcturus at a distance of 243 light years, and hence appears far fainter in the skies of Earth.
Omicron Boötis is an evolved yellow star that has consumed its reserves of hydrogen, and is now in the part of its life cycle in which its core fuses atoms of helium to create carbon. Its outer atmosphere has inflated to more than ten times the diameter of the Sun, but exists in a tenuous and comparatively cool form. The star is far more luminous than the Sun, generating some seventy times as much light energy.
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