ALPHA HERCULIS

'Alpha Herculis' (α Her / α Herculis) is a multiple star in the constellation Hercules. It also has the traditional name 'Ras Algethi' or 'Rasalgethi' (Arabic: رأس الجاثي ra's al-jaθiyy Head of the Kneeler), and the Flamsteed designation '64 Herculis'.
When viewed through a telescope, this system is resolved into two components designated α¹ and α². These two components are more than 500 astronomical units apart, with an estimated orbital period of approximately 3600 years. α¹ is a relatively massive red bright giant. α² is actually a double star system with a primary yellow giant star and a secondary, yellow-white dwarf star. (These components are sometimes designated α Herculis A, Ba and Bb, respectively.)
The angular diameter of the red giant α¹ has been measured with an interferometer as
34 ± 0.8 milli-arcseconds, or 0.034 arcseconds.^[1] At an estimated distance of 120 parsecs, this corresponds to a radius of about 300 million kilometers (or 188 million miles),^[2] or 400 times the size of the Sun. It has a total of about 14 solar masses,^[3] and has emitted a sparse, gaseous envelope that extends at least 90 astronomical units.^[4]
The star is located at the bottom of the constellation. The traditional name "Head" comes from the fact that in the antiquity Hercules was depicted upside on the constellation maps.

Contents

References

See also

External links

References

1. The infrared angular diameter of Alpha Herculis measured with a Michelson interferometer, Benson, J. A.; Dyck, H. M.; Mason, W. L.; Howell, R. R.; Ridgway, S. T.; Dixon, D. J., , , Astronomical Journal, 1991
2. Rasalgethi
3. The Bright Star Catalogue, , D., Hoffleit, Yale University Observatory, 1982, —See note 6406.
4. The Circumstellar Envelope of Alpha Herculis., , Armin J., Deutsch, Astrophysical Journal, 1956

See also

★ List of largest known stars

External links

★ Dome-of-theSky entry (Retrieved 2 February 2007)

★ Alcyone entry (Retrieved 2 February 2007)