A Selection of Double Stars in Orion
January 2007 :
The Astronomical League, composed of over 240 local astronomical societies and numerous individual at-large members, is one of the largest amateur astronomical organizations in the world. Its basic goal is to promote public interest in amateur astronomy. To that end, the Astronomical League awards certificates to members who observe a specific set list of sky objects (Messier or Herschel objects, for example).
One of these certificates is for Double Stars. Of the one hundred double and multiple stars on the Astronomical League’s list, nine are found in Orion. Try your luck with them, then go to www.astroleague.org to see the complete list. Beta Orionis (Rigel) magnitudes 0.1 and 6.8, separation 9.5 arcseconds A fine test for small-aperture scopes, because the companion hides in the glare of the main star. Use the highest practical magnification.
Delta Orionis mags 2.2 and 6.3, sep 52.6” Westernmost star in Orion’s belt; resolvable in binoculars.
Struve 747 mags 4.8 and 5.7, sep 35.7” Another binocular pair. In telescopes, appears in the same low-power field as iota Orionis.
Lambda Orionis mags 3.6 and 5.5, sep 4.4” A delicate little pair, best seen with 75 – 90X.
Theta 1 Orionis mags 6.7, 7.9, 5.1, and 6.7, seps 8.8”, 13”, 21.5” The “Trapezium,” by far the finest multiple star in the night sky. Located in the brightest part of the Orion Nebula, these stars are the progeny of this great gas cloud. Magnificent!
Iota Orionis mags 2.8 and 6.9, sep 11.3” Fine pair that sports the white and blue colors typical of many Orion doubles.
Theta 2 Orionis mags 5.2 and 6.5, sep 52” A wide binocular pair located on the edge of the Orion Nebula.
Sigma Orionis mags 4.0, 7.5, and 6.5, seps 12.9” and 43” Nice, wide triple. Use low power.
Zeta Orionis mags 1.9, 4.0, and 9.9, seps 2.4” and 58” Most easterly of Orion’s “belt” stars. The close pair is a difficult split for small scopes. Use high power on an evening when the seeing is excellent.
And, finally, just to bring to ten the number of double and multiple stars on our Orion list, I add a personal favorite.
Struve 817 Orionis mags 8.2 and 8.3, sep 18.5” This faint, but pretty pair is located just 1/3 degree south of Betelgeuse. A fine sight when captured in the same low-power field as this great star.
