One of the celestial highlights of this season has to be the southern Milky Way, ranging down from Orion through Canis Major and into points far south. The region, especially in Canis Major and neighboring Puppis, is rife with open clusters, a veritable celebration of stars and star cities. This month’s targets represent only a tiny sample of what’s available. So this time of year, if you have time, pay a visit to this part of the Milky Way. It isn’t up long due its southern location, but it’s definitely worth the visit. And as always, enjoy!

NR CMa   rating EASY
   variable star in Canis Major
   RA 07h 27.1m  Dec -17d 51.9′  (2000)
   Magnitude 5.6

Some stars, like some people, just have a lot going on. NR CMa lies in Canis Major almost due east of Sirius, practically on its eastern border with Puppis. As the name suggests NR is a variable, of the Delta Scuti (dwarf cepheid) class, with a 16-hour magnitude range of 5.67 to 5.70 – not a variation you’ll catch with casual observing! Delta Scuti stars are main sequence variables that are the second most abundant variable source in the Milky Way after white dwarfs.

NR is also a difficult double star, ADS 6093, consisting of a magnitude 5.7 primary and magnitude 11.2 companion which were 2.4″ apart in 1878, and 1.6″ apart in 1972.

Perhaps most interesting, though, is that NR will be paying us a visit in the near future, astronomically speaking. Eventually, in just 2.6 million years, it will become the brightest star in our sky, and will retain that distinction until 3 million years from now (mark your calendar!). At its brightest, in 2.87 million years, NR will be just 14 light years away and will reach magnitude -0.88, about the same as Canopus today. NR will eventually surrender its title to Omicron Herculis, but by then it will have joined 3 other stars in Canis Major that have reigned as the brightest star. These include Sirius (current), as well as Beta CMa (4.5 to 3.7 million years ago), and Eta CMa (which immediately preceded Beta from 5 to 4.5 million years ago).

For those of you with catalog fetishes, NR is also known as SAO 152894 and HR 2853. It has about 1.5 solar masses, is about 2 billion years younger than the Sun, and is currently 85.88 parsecs (280 light years) away.

NGC 2360   rating MEDIUM
   open cluster in Canis Major
   RA 07h 17.8m  Dec -15d 37.5′  (2000)
   Magnitude 7.2

Known as Caroline’s Cluster, NGC 2360 was discovered on Feb. 26 1783 by Caroline Herschel. She described it as “a beautiful cluster of pretty compressed stars near 1/2 degree in diameter.” The cluster was her first original discovery of a deepsky object, and it was included in her own list as No. 2. But her notes were overlooked until her brother William included the cluster in his 1786 catalog of 1000 clusters and nebulae as H VII.12 and acknowledged her as the discoverer.

NGC 2360 lies 3.5 degrees east of Gamma CMa, along with many other open clusters in the area, in the midst of the southern winter Milky Way. The cluster contains one or possibly two blue stragglers, has a diameter of around 15 light-years, and is about 3700 light-years away. At magnitude 7.2, NGC 2360 is bright enough to spot in binoculars. It’s also compact, which translates to a high surface brightness. So it’s easy to find even in moderately light-polluted skies.

Abell 21   rating HARD
   planetary nebula in Gemini
   RA 07h 29.0m  Dec +13d 15.0′  (2000)
   Magnitude 16, 10×6′

Abell 21, also known as the Medusa nebula, is a large old planetary in southern Gemini, near its border with Canis Minor. In fact, the nearest bright marker star is 2.8-magnitude Beta CMi, or Gomeisa. From Gomeisa, a 5-degree trip due north into Gemini should land you on almost top of
Abell 21.

Also known as Sharpless 2-274 and PK 205+14.1, the Medusa nebula is a challenging planetary for observers. Although large for a planetary, its surface magnitude is very faint, reported as anywhere from 15 to 25. The planetary is quarter-moon shaped; its SE end is round and its NW side is flattened, the brightest area being the SW “limb.” Several stars (11-14th mag) are embedded. In general an 8-inch scope is the minimum recommended weapon to corner this catch, and a 10-inch with an oxygen III (OIII) filter will find it easily.

The Medusa was discovered in 1955, and until the early 1980s it was thought to be a supernova remnant. It lies about 1500 light-years away, roughly 1/2 the distance of the Ring nebula, M57, in Lyra.