By Brian Cuthbertson
If you’re a galaxy aficionado, your sky is rising in the evening this time of year. The winter Milky Way still reigns in the west, but in the east the deep space window, from Ursa Major down through Hydra, is now wide open to the more distant universe. Don’t write off the winter sky just yet though – the southern winter Milky Way is a wonderful land to get lost in – star fields and clusters galore if you drop down to Canis Major and vicinity. Whatever your tastes, you can find it up there. Enjoy!
ADS 5951 rating EASY
bright double star in Canis Major
RA 07h 16.6m Dec -23d 18.9′ (2000)
Magnitude 4.8
Here’s a delightful double star that can be easily found SE of Sirius and 4 degrees ENE of Delta CMa. Also designated h3945 and 145 Cma, the star resembles a fainter version of the well-known summer double Albireo in the tail of Cygnus. It is in fact sometimes called the “Winter Albireo”, but with perhaps even stronger color tints.
The vivid ruddy orange primary (mag. 5.0 K0) and its greenish-blue type companion (mag. 5.8 F0) are separated by an easy 27″. The colors are striking even in a 3-inch scope at 30x, and are spectacular in a 6-inch at 50x. Some observers consider the star even more beautiful than its namesake Albireo.
The star’s designation h3945 indicates that it’s one of 5500 double stars cataloged by John Herschel (William’s son) in the early 1800s. The ADS designation comes from American astronomer Robert Aitken’s (1864-1951) massive two-volume catalog of double stars within 120 degrees of the North Pole (ie, north of -30 degrees declination). The catalog was published by the Carnegie Institution in 1932 and contains 17,180 double star measurements.
NGC 3359 rating MEDIUM
spiral galaxy in Ursa Major
RA 10h 46.7m Dec +63d 13.2′ (2000)
Magnitude 10.5
Ursa Major is a galaxy haven; the sky in and around the bowl of the Big Dipper is a happy hunting ground for deepsky galaxy observers. NGC 3359 lies just outside the bowl, about 2.5 degrees WNW of 2nd magnitude Alpha UMa (Dubhe) which marks the bowl’s NW corner. Since there are no other galaxies of any size or brightness in the immediate area, identifying it shouldn’t be difficult.
In a 6-inch scope the galaxy is a diffuse 2×1.5′ glow elongated N-S. The size grows to 6×4′ in a 12-inch class scope, but with a low surface brightness its outer regions are hard to trace.
Located about 49 million light years away, NGC 3359 is an evolving barred spiral: the galaxy’s general stellar population is several billion years old, but images shows a short central bar much younger than that. The stars in the bar are only about 500 million years old – much younger than the rest of the galaxy. Some astronomers have predicted that the galaxy may eventually look like barred spiral NGC 1300 in Eridanus, which suggests that the bar could grow until it becomes a dominant feature of the system.
NGC 3356 has many HII regions with active star formation – over 100 of them by some estimates. Deep images also show two very faint arms that wrap most of the way around the system.
NGC 2346 rating: HARD
“Butterfly” type planetary nebula in Monoceros
RA 07h 09.4m Dec -00d 48.4′ (2000)
Magnitude 10.8; diameter 55″
Easily found about 40 arc minutes southwest of 4th-magnitude DELTA Monoceros, NGC 2346 is an example of a bipolar planetary. It is informally called a “Butterfly” planetary because of its appearance. Other planetaries also dubbed “Butterfly” include NGC 6302 in Scorpius and planetary M-29. So remember that “Butterfly” is effectively an informal planetary nebula class and not a name; there is no unique object called the “Butterfly” planetary. But NGC 2346 does also have its own nickname: the “Hourglass.” Whatever you may call it, it’s an interesting object.
NGC 2346 is an example of a planetary with a central star that can outshine the nebula itself. The star is actually a spectroscopic binary consisting of the bright A5 star we see plus a very hot O subdwarf that excites the nebula to glow. Until 1981 the binary was roughly constant at 11, varying over its 16-day orbital period. But then it began generally dimming until it was down nearly to 15th mag by 1984. By 1986 it was back to normal at 11. This odd behavior is due to a combination of mutual eclipses of the two stars, plus moving opaque dust clouds ejected from the O subdwarf that occasionally obscure the system until the clouds eventually disperse. The binary now has the variable name V651 Mon.
Visually, NGC 2346 is small, faint and difficult to observe due to its bright central star. Telescopes in the 6- to 8-inch class will show what looks like an 11th magnitude star surrounded by a small, faint halo. Larger scopes may detect a slight pinching in the nebula, which gives the planetary its colorful aliases. Both UHC and OIII filters will help bring out detail; an OIII filter for example dims the central star while enhancing the nebula itself. The system lies about 4300 light years away.
