Alpha Herculis


Distance (Light Years) 382 ± 126
Apparent Magnitude 2.78
Color (B-V)1.44

Names For This Star

Rasalgethi (alternatively Ras Algethi or Rasalegti) derives from the Arabic name for the star Al Ras al Jathiyy, "The Kneeler's Head". The name reflects the way that the constellation of Hercules is usually seen as a kneeling man.

Description of the Star

Rasalgethi is a cool, red M5Ib-II bright giant or supergiant perhaps 900 times as luminous as the sun and maybe 300 times the diameter of the sun.

Rasalgethi is a multiple star system. The companion Rasalgethi B is itself a binary star. The B star revolves at a distance of 4.8 arc sec from A, that is, about 570 AU with a period of 3600 years.

Rasalgethi A was discovered by Sir William Herschel to be a variable star in 1795. The star varies about 1 magnitude on the time scale of 50 to 150 days.

The star is surrounded by an expanding envelope of material stretching out to about 900 AU from the star. It is estimated that the rate of mass loss is 0.3% of the mass of the sun in 100,000 years.

Other Designations For This Star


64 Herculis

Hipparcos Identifier (HIP Number)


Harvard Revised (HR Number)


Henry Draper Catalog (HD Number)


Bonner Durchmusterung (BD Number)

BD+14 3207
Smithsonian Astrophysical
Observatory compendium (SAO Number)

Fundamental Katalog (FK5 Number)



Copyright © 1998 - 2010 by Arnold V. Lesikar,
Professor Emeritus
Dept. of Physics, Astronomy, and Engineering Science,
St. Cloud State University,St. Cloud, MN 56301-4498

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