Double Stars in Orion
Beta (b) Orionis, better known as Rigel, is one of the brightest stars in the sky. A companion 1/400 as bright lies just 10 arcseconds to its south, creating one of the most spectacular magnitude-contrast pairs in the heavens. Like most of the stars in Orion, both are hot B-type suns. In 1949, Sky & Telescope columnist Leland Copeland described Rigel as “a blue boy with a companion on his shoulder.” A 3-inch scope at 90x will show the little star on a steady night, but the larger the telescope, the more dramatic the effect. The view at 150x in a 14-inch scope is never to be forgotten!
Theta1 (q1) Orionis
The six brightest components of the Trapezium show well in this photograph from the Hubble Space Telescope.
Courtesy J. Bally, D. Devine, R Sutherland, and D. Johnson, NASA.
is the famed multiple-star system lying at the heart of the magnificent Orion Nebula. Its four brightest components range from 5th to 7th magnitude, and even the smallest scopes resolve them into an irregular quadrilateral commonly called the Trapezium. These hot, newborn, O
- and B
-type suns shine bluish white like diamonds against the green of the nebula itself. Some observers even report seeing them suspended in front of the nebulosity, resulting in an amazing 3-D effect! Take a look and see if you do too.
Double stars’ components are usually named in order of brightness, but the bright Trapezium stars are lettered A, B, C, and D in order of right ascension, with C being the brightest. They are actually the most obvious members of a star cluster in formation. On a night of steady seeing, apertures as small as 4 inches will show the 11th-magnitude E and F stars. Much larger apertures are required to see components G and H. The A and B stars are eclipsing binaries with periods of 65 and 6.5 days, respectively.
Sigma (s) Orionis
The fine quadruple star Sigma (s) Orionis shares a high-power eyepiece field with the faint triple Struve 761. North is up.
Sky & Telescope illustration.
is an amazing multiple-star system. Most amateur instruments will reveal a beautiful quadruple. Instead of a box-shaped configuration like the Trapezium, Sigma’s components are strung out in an irregular line with the 4th-magnitude primary near one end. Here again, all the stars are blue-white O
- and B
-type suns, but Sigma is often described as a colorful multiple system. Among the various hues reported here by both classical and modern observers are yellow, orange, red, grape red, ash, and pale gray. Adding to the beauty of the scene is Struve 761, a slender triangle of 8th-magnitude stars lying 210 arcseconds northwest of the Sigma complex. All the stars in this area appear to be moving through space together, forming a miniature star cluster.