Sky Object of the Month – February 2017
(Courtesy LVAS Observer’s Challenge*)
h3945 – Double Star in Canis Major (Mags. 5.0 + 5.8; Sep. 26.4”; P.A. 52o (2008)
What is the most colorful double star in the night sky? Most amateur astronomers would vote for Albireo (beta [b] Cygni. Others might cite gamma (g) Andromedae, iota (i) Cancri, xi (x) Bootis, or eta (η) Cassiopeiae. Sadly overlooked is a double star that might challenge them all – h 3945 in Canis Major. It is arguably the most colorful double star in the winter sky and, in fact, has been nick-named the “Winter Albireo.”
h3945 (aka 145 Canis Majoris) is one of more than 5500 double stars catalogued by John Herschel (William’s son) in the early 1800s. The magnitude 5.0 primary is accompanied by a 5.8 magnitude companion 26.4 arc-seconds away. Their spectral types (K3 and F0) give rise to a stunning color contrast. In her book Double Stars for Small Telescopes, Sissy Haas writes, “Showcase pair: A bright, wide, and easy pair with deep colors. The stars are bright citrus orange and royal blue; these colors are seen vividly and in strong contrast.” In early 2008, 3945 was the subject of a forum on the Cloudynights website. The general consensus was that this is one of the most beautiful double stars in the night sky. That was my thought when I included h3945 in a “Top 100 Doubles” series written for Deep Sky Magazine in 1983.
Despite these kudos, h3945 still gets the cold shoulder from most backyard astronomers. In the February, 1980, issue of Deep Sky, I described h3945 as “one of the most colorful, yet underrated, double stars in the heavens.” Richard Dibon-Smith, on his Constellation Web Page (www.dibonsmith.com) concurs, noting that, “h3945 is a gorgeous yet rather unknown binary.” In the Cambridge Double Star Atlas, co-author James Mullaney laments that h3945 is “Largely unknown & unobserved – a pity!”
Why would such a beautiful double star be so grossly ignored? There are two parts to the answer – h3945 is in a southerly location, and it isn’t as bright and easily located as Albireo or Almach. The first isn’t a problem if your observing site affords a clear view of the lower half of Canis Major. Because h3945 is marginally visible to the naked eye from mildly light-polluted suburban skies, the accompanying finder chart will help you find it.
Sissy Haas, Richard Dibon-Smith, James Mullaney, your truly, plus a batch of backyard astronomers on the Cloudynights website have all raved about h3945. Now it’s your turn to experience one of the night sky’s true gems.
Glenn Chaple for the LVAS
*The purpose of the LVAS Observer’s Challenge is to encourage the pursuit of visual observing. It is open to everyone that is interested, and if you are able to contribute notes, drawings, or photographs, the LVAS will be happy to include them in our monthly summary. If you would like to contribute material, submit your observing notes, sketches, and/or images to either Roger Ivester (firstname.lastname@example.org) or Fred Rayworth (email@example.com). To find out more about the LVAS Observer’s Challenge or access past reports, log on to lvastronomy.com/observing-challenge.