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Alpha Herculis
Multiple star system in the constellation Hercules
Alpha Herculis (α Herculis, abbreviated Alpha Her, α Her), also designated Rasalgethi and 64 Herculis, is a multiple star system in the constellation of Hercules. Appearing as a single point of light to the naked eye, it is resolvable into a number of components through a telescope.
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It has a combined apparent magnitude of 3.08, although the brightest component is variable in brightness. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 360 light-years (110 parsecs) distant from the Sun. Five degrees east-south-east of Rasalgethi lies Rasalhague, the brightest star in Ophiuchus. These stars may be among the closest-lying pair of alpha stars in the entire sky. Despite the star designated as "alpha", it is actually the 5th brightest star in Hercules. Alpha Herculis is a triple star system. The primary (brightest) of the three stars, designated α Herculis or α Herculis A, is a pulsating variable star on the asymptotic giant branch (AGB). The primary star forms a visual binary pair with a second star, which is itself a spectroscopic binary.
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