Alpha Bootis


Distance (Light Years) 36.7 ± 0.3
Apparent Magnitude -0.05
Color (B-V)1.23

Names For This Star

"Arcturus" is a Greek word meaning "Bear Guard." This name for the star is undoubtedly connected with it's position just to the east of the Ursa Major, The Greater Bear.

Another name for the star is Haris-el-sema, from the Arabic Al Haris al Sama, "The Keeper of Heaven.

Description of the Star

The Hipparcos Catalogue mission discovered Arcturus to be a binary star system. Arcturus A is an orange colored giant K1.5IIIFe-0.5 star. The spectral type implies an effective temperature of the star is about 4300 K and a mass about 20 times that of the sun.

The Apparent Magnitude and distance indicate a luminosity 110 times that of the sun. The star has about 28 times the diameter of the sun.

The companion Arcturus B is about 3.3 magnitudes dimmer than A. At 0.255 arc sec of separation, the projected distance between the stars is 2.9 AU.

According to Burnham, Arcturus is the fourth brightest star in the sky.

Other Designations For This Star


16 Bootis

Hipparcos Identifier (HIP Number)


Harvard Revised (HR Number)


Henry Draper Catalog (HD Number)


Bonner Durchmusterung (BD Number)

BD+19 2777
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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