Let Mars be your guide to no fewer than 15 diverse and delightful double stars that pepper its path through Scorpius and Libra this opposition season.
Mars strides to opposition this weekend, cruising westward in retrograde motion across northern Scorpius. At magnitude –2.0, the planet burns like a red-hot coal, calling attention to itself like no other "star" in the evening sky. Telescopic observers will enjoy a plumped-up disk better than 18″ across, the largest Mars has appeared in more than 10 years. So long as the atmospheric seeing is steady, the planet will serve up a host of dark markings, mists and clouds in telescopes as small as 4-inches.
This week and early next, the nearly full Moon will make deep-sky viewing nearly impossible, but Mars will be untouched, as will that other category of stellar gems, double stars. Neither is affected much by moonlight, so bring it on.
By good fortune, Mars happens to lie in a double star-rich region of the nighttime sky. So when you're done observing the Red Planet or if poor seeing prevents a crisp view, let Mars be your guide to a delightful mix of stellar duos.
A circle with a radius of 7° centered on the planet corrals some 15 double stars that range from Beta (β) Scorpii, one of the easiest and prettiest binaries in the entire sky, to the challenge of Antares. Or how about the deliciously obscure Scorpius "double-double" Sh 225 and Sh 226? These and more await your attention the next time you drop in on Mars.
I had a thoroughly good time with the whole bunch — with Mars tossed in for good measure — during a single night's observing session with my 10-inch "star cleaver" recently. 76× proved ideal on eight of the pairs; for the remainder, I had to employ 212× as my optical crowbar. Even a 6-incher should split every one save 47 Librae. Click the map above, save it to your desktop and make a printout for use at the telescope.
Beta Scorpii, a.k.a. Graffias, is hands down the brightest, gemmiest double and the first you should show off to guests and friends. I've split Antares just twice: once in a antique 6-inch Brashear refractor and a second time when the star was occulted by the waning Moon. Moments before Antares made its appearance, I briefly caught sight of the 5th-magnitude companion at the lunar limb shielded from the primary's ferocious glare. With the help of our satellite, I finally put the bully supergiant in its place!
Only one star, 47 Librae, remained unsplittable. I'm hoping a better night and higher magnification will do the trick. Nu (ν) Scorpii makes for a neat sight. At low power it's an undistinguished wide pair, but jack up the magnification and each divides again to make a pair of pairs rivaling the Double-Double Epsilon 1,2 Lyrae. Early 20th-century astronomer Agnes Clerke wrote in 1905 that Nu was “perhaps the most beautiful quadruple group in the heavens.” Each doublet has widened since then and can be split these days in a 5-inch scope.
I get a bang out of doubles that are widely separated in magnitude for the pleasure of seeing two radically different-sized stars sharing a lifetime together. Some pairs are so unequal the companion seems to hide in plain sight like a shy child standing behind her parent's legs. Good examples of these include 2, 12, and β38 Scorpii. If equal pairs are your thing, check out β122 Librae.
I'll gladly step away from the eyepiece now so you can have a look.
|Star names/designations||Mags.||SEParation||R. A.||DEC.||Comments|
|S 672 Librae||6.3, 8.9||11″||15h 32m||–20º 10′||Close, low power pair|
|β122 Librae||7.6, 7.8||1.7″||15h 40m||–19º 46′||V. tight, equal, ×212|
|β354 Librae||7.3, 9.3||6″||15h 43m||–25º 25′||Unequal, nice at 125×|
|2 Scorpii||4.7, 7.0||2.1″||15h 54m||–25º 20′||Comp v. close at ×212|
|47 Librae||6.0, 8.0||0.55″||15h 55m||–19º 23′||Maybe next time!|
|β38 Scorpii||7.2, 9.5||4″||16h 03m||–25º 01′||Unequal and close|
|Graffias (Beta Scorpii)||2.6, 4.5||14″||16h 05m||–19º 48′||Sumptuous maximus!|
|Omega (ω) 1,2 Scorpii||4.0, 4.3||720″||16h 07m||–20º 40′||Optical n. eye double|
|Nu Scorpii||4.4, 5.3 /
|16h 12m||–19º 48′||"Southern" Eps Lyrae|
|12 Scorpii||5.8, 8.1||4″||16h 12m||–28º 25′||Close, unequal|
|Sh 225||7.4, 8.1||47″||16h 20m||–20º 03′||Fine pair w/ Sh 226|
|Sh 226||7.5, 8.3||13″||16h 20m||–20º 07′||Great at low power|
|Sigma Scorpii||2.9, 8.4||20″||16h 21m||–25º 36′||Golden primary|
|Rho (ρ) Ophiuchi||5.1, 5.7||2.9″||16h 26m||–23º 27′||Superb, in nice field|
|Antares||1.1, 5.4||2.5″ in
|16h 29m||–26º 26′||Challenging|
* Data from the Cambridge Double Star Altas