Some Bright Autumn Double Stars
October 2005 :
Autumn is a season of promise for the stargazers. The nights are getting longer, the air clearer, and those pesky summer mosquitoes are a thing of the past. In a few months, Orion and his magnificent wintry retinue will take center stage. While the autumn night sky appears devoid of bright stars, it’s still home to a rich array of double stars. Here are ten of the best:
alpha1, alpha2 Capricorni (alpha1, magnitudes 4.2 and 9.2, separation 45.4 arcseconds; alpha2, mags 3.6 and 9.3, sep 154.6”) The magnitude 4.2 (alpha1) and 3.6 (alpha2) stars form a naked eye pair separated by 376”. A 3-inch scope will capture their 9th magnitude companions.
gamma Delphini (mags 4.5 and 5.5, sep 9.6”) The Dolphin’s “snout.” One of the finest double stars for small-aperture telescopes. Can you detect the pair’s subtle yellow and blue colors? In the same field, ¼ degree to the southwest, is the delicate little pair Struve 2725 (mags 7.6 and 8.4, sep 5.8”).
61 Cygni (mags 5.2 and 6.0, sep 30.5”) This binary pair is historically important as the first star whose distance was accurately determined (Bessel – 1838). Both stars appear golden yellow.
Struve 2816 and Struve 2819 Cephei (Struve 2816, mags 5.6, 7.7, and 7.8, sep 11.7” and 19.9”; Struve 2819, mags 7.5 and 8.5, sep 12.4”) A triple star and double star in the same low-power field. Grand sight!
epsilon Pegasi (mags 2.4 and 8.4, sep 142.5”) An optical, or line-of-sight, double. What makes this pair so interesting is the apparent pendulum-like motion of the fainter star when the telescope is gently rocked in a direction perpendicular to a line connecting the two stars. Fascinating effect!
zeta aquarii (mags 4.3 and 4.5, sep 2.2”) A beautiful twin binary that is slowly widening from a minimum separation of 1.7” in 1977. Use at least 100X for a comfortable split.
sigma Cassiopeiae (mags 5.0 and 7.1, sep 3.0”) A tough “split” for small scopes, because of the two-magnitude difference in magnitude of the component stars. Just one degree north is the remarkably rich open star cluster NGC 7789.
eta Cassiopeiae (mags 3.4 and 7.5, sep 13.0”) What makes this slow-moving binary pair (period = 480 years) noteworthy is its stunning color scheme – yellow for the primary star, red for the companion. Marginally visible in small instruments, the colors really stand out in a 6-inch scope.
alpha Ursae Minoris (mags 2.0 and 9.0, sep 18.4”) Polaris, the North Star. This is a classic light test for the common 60mm refractor. The 9th magnitude companion is hard to spot in the glare of the bright primary star. Easy in a 6-inch scope; shows yellow and blue colors.
gamma Arietis (mags 4.8 and 4.8, sep 7.8”) A grand “twin” pair, both white. Their telescopic appearance, like gleaming cat’s eyes or the headlights of a distant automobile, are mesmerizing!
