Canis Major is an ancient constellation. It is one of the two dogs accompanying Orion the hunter (the other one of course being Canis Minor) and it is chasing the hare at Orion’s feet. Puppis was part of the equally ancient constellation Argo Navis, the ship of the Argonauts. The break up of Argo Navis was proposed in the nineteenth century, and was formally achieved when the IAU finalised its list of constellations in 1930, despite Argo Navis receiving an official abbreviation (Arg) in 1922. Puppis (the Stern) is the largest and most northern part of the former constellation, but we can only see about a third of it from the UK. 

This is a good opportunity to say something about the visibility of deep sky objects. In theory, we can observe stars down to a declination of 39 degrees south (i.e. 51-90), but several things prevent us from seeing so far south. Stuff gets in the way unless you are sailing on a calm ocean: trees, houses and such like. An average 10-metre-high house 40 metres away knocks 14 degrees off what you can see. Then there is extinction, as the star has to travel through a greater mass of air to reach your eye. Adhara (Epsilon Canis Majoris) is a bright 1.5 magnitude star, but even at its maximum height in the UK, it is dimmed to magnitude 2.2. Add the fact that local light pollution is worse near the ground, and the problem is multiplied. Finally, if a star (or other deep sky object) has a low declination, we can only observe it when it is in the south. To take Adhara, for example; it is only visible for a period of about three hours.

Sirius is the brightest star in Canis Major; and the brightest star in the sky, with a magnitude of -1.3. A hot A type star, its absolute magnitude is an unremarkable 1.4, but it is also very close to us, being only 8.7 light years away. It has a famous white dwarf companion Sirius B, which was predicted to exist before it was observed by the telescope maker Alvan Graham Clark in 1862. The ”pup” is in fact not that close to Sirius, but the glare of the main star makes observing it difficult (Clark found it when the main star was blocked by a nearby building). At the moment it is at its maximum separation of 11.3 arcseconds, and hence this is a good time to try to see it.

Just four degrees below Sirius is Messier 41 [1] which is a lovely cluster, which looks like the symbol of the Isle of Man, the triskelion - or perhaps a spider. However, although it is relatively bright (magnitude 4.5) and at least in theory easily located, I have had trouble finding it sometimes, probably a result of its low declination. It is about 190 million years old and 2,300 light years distant from us. If it were higher in the sky, it would be a splendid sight. Three degrees east (or left) of Muliphein is Caroline’s Cluster (Caldwell 58) [2], discovered by Caroline Herschel in 1783, which is dimmer and smaller than Messier 41. There is a group of stars surrounding Tau Canis Majoris [3], NGC 2362 or Caldwell 64, which lie on the boundary between multiple stars and a cluster. It is called the Mexican Jumping Bean, because if you look at it through a telescope and then knock its tube, the ring of stars round Tau CMa appear to wobble while the main star stays still. This is a persistence-of-vision effect similar to the Pendulum Star Enif (see Pegasus). Just over a degree to the east (left) of Tau CMa is VY Canis Majoris, which is a pulsating red hypergiant and a Mira-type variable; its magnitude range (6.5 to 9.6) is similar to Mira in Cetus. It is one of the largest stars in our galaxy, being 1,400 times larger than our Sun.

There is one easily observed double star in Canis Major, namely 145G Canis Majoris or HJ 3945 [4]. It is called 145G because it was one the stars numbered by the American astronomer Benjamin Apthorp Gould in the nineteenth century, not John Flamsteed. Gould, incidentally, was one of strongest advocates for the breaking up of Argo Navis. It is sometimes called the Winter Albireo as it is a deep yellow and blue double separated by 26.5 arcseconds. The two stars are of similar brightness (mag. 5.0 and 5.8). 

There are only two naked-eye stars in Puppis that can be seen from Havering, and I have simply drawn a line between them. Tureis (Rho Puppis) is a 2.8 magnitude variable star. Xi (or Ksi) Puppis, now called Azmidi (formerly Asmidiske), is a 3.3 magnitude yellow supergiant which is similar to Wezen, a 1.8 magnitude yellow supergiant in Canis Major. Thanks to their low declination, they both look like misty yellow stars in a telescope. Near Azmidi, there are two nice double stars which are dogged by confusion about their names. k Puppis [5] has two white stars with a similar brightness (mag. 4.4 and 4.6), with a relatively narrow separation of 10 arcseconds. n Puppis [6], which lies above k Puppis, has two pale yellow stars, also of similar brightness (mag. 5.8 and 5.9). 

Three schematic depictions below - Stella Doppie database.

There are three notable star clusters in the visible portion of Puppis, which extends some thirteen degrees above Tureis to its boundaries with Hydra and Monoceros. Messier 46 [7] is a fairly compact magnitude 6 cluster, which is almost 5,000 light years away and 251 million years old. It was discovered by Charles Messier in 1771. By coincidence, there is a faint circular planetary nebula, NGC 2438, superimposed on it, as it is only 1,370 light years distant. It is difficult to see visually, but appears in images of M46. Only a degree away to the west is Messier 47 [8], which is both closer (1,600 light years) and younger (78 million years) than its neighbour. If you start with M47 and stop the tracking on your telescope, M46 will drift into view about five minutes later. Visually it is more open and brighter (at mag. 4.4); it is also larger being about the same size as the full moon.

M47 was discovered by Giovanni Batista Hodierna in the mid-seventeenth century (when he also discovered the star clusters in Auriga), and re-discovered over a century later by Caroline Herschel. It was a lost Messier object until it was realised in 1959 that Messier had erroneously swapped the plus and minus signs in his coordinates. Near Azmidi, and about nine degrees below M46, is Messier 93 [9]. It is as bright as M46 but it is the smallest of the three, being only half the size of M46; it has been described as having the appearance of a starfish. It is also the same distance and age as M46.