Some Bright Summer Double Stars
June 2005 :
In this modern era of the huge galaxy-gulping Dobsonian reflector, double stars have become the neglected children of the cosmos. That’s too bad, because few heavenly objects have the visual appeal of double stars. There’s something almost magical about the sight of two stars shining side-by-side against the inky black backdrop of space. The following list describes ten of my favorite summertime double stars. Why not set aside your galaxies and globular clusters for an evening or two and give these delightful duos a look-see? Perhaps you’ll agree with me – double stars are twice the fun!
Epsilon Bootis, Izar (magnitudess 2.7 and 5.1, separation 2.9 arcseconds) Izar’s striking gold and blue colors inspired its discoverer, F. G. W. Struve, to nickname it Pulcherrima – “the most beautiful.” Can be resolved in a three-inch scope, if the seeing is steady and you use 100X or more.
xi Bootis (mags 4.8 and 6.9, sep 6.5”) Binary system (Period ~ 150 years) with remarkable yellow and red colors. Closing to a separation of 2.2” in 2064.
beta Scorpii (mags 2.9 and 5.1, sep 13.6”) A beautiful pair, easy in small scopes. The primary (brighter component star) is white; its partner (secondary) seems blue or blue-green.
mu Draconis (mags 5.8 and 5.8, sep 2.2”) A neat twin binary star (Period = 482 years) whose separation is very slowly increasing. The two lie at the theoretical limit of resolution for the common 60mm (2.4-inch) refractor. If you attempt to “notch” mu Dra with such a scope, you’ll need your highest magnification (about 120X for that aperture) and optimum seeing conditions.
36 Ophiuchi (mags 5.3 and 5.3, sep 4.6”) Another twin binary (Period = 549 years), but with a wider separation that makes these golden yellow stars easy to resolve in small-aperture instruments. At a distance of “only” 18 light-years, 36 Oph is a relative neighbor of ours.
alpha Herculis, Rasalgethi (mags 3.1v and 5.4, sep 4.9” ) Don’t expect to see this binary pair complete an entire orbit – they take 3600 years to do the job! This duo, with its colorful orange and blue-green components, is a favorite of double star enthusiasts. The primary is a semi-regular variable star.
nu Draconis (mags 5.0 and 5.0, sep 61.0”) The faintest star in a quadrangle that forms the head of Draco. Not all double stars require a telescope, and nu Draconis is proof. It’s a pretty sight when viewed with binoculars.
70 Ophiuchi (mags 4.3 and 6.0, sep 5.0”) This rapidly moving binary (Period 88 years) has undergone tremendous changes in the past few decades. Now widening to a maximum separation of about 7 arcseconds in 2020.
epsilon Lyrae (mags 5.1 and 6.0, sep 2.4”; mags 5.1 and 5.4, sep 2.2”) The celebrated “Double-double. These two pairs – each a slow binary system - are 210 arcseconds apart, a separation that eagle-eyed individuals can discern with the unaided eye. All four stars can be glimpsed in a 60mm refractor at 120X
beta Cygni, Albireo mags 3.2 and 4.7, sep 34.3 arcseconds) I’ve saved the best for last. This beautiful topaz yellow, sapphire blue pair is probably the most-viewed of all double stars. It’s a favorite at star parties, especially is you want to prove to a newcomer that all stars are not white. I find the colors appear most vivid when Albireo is viewed with small-aperture scopes.
