Puppis the Stern

Sternforward Argo by the Great Dog’s tail

Is drawn; for hers is not a usual course,

But backward turned she comes, as vessels do

When sailors have transposed the crooked stern

On entering harbour; all the ships reverse,

And gliding backward on the beach it grounds.

Sternforward thus is Jason’s Argo drawn.

~Aratos

Puppis lies directly east of a line joining Sirius and Canopus. It is a large constellation with an area of 673 sq.º, formed by B. Gould in 1877 from the larger group of Argo Navis. With the Milky Way flowing right through Puppis, the starfields are very rich and grand. Therefore, almost all the galaxies in this region are obscured and many of the open clusters blend into this background carnival of stars.

The brightest star in Puppis is zeta at magnitude 2.25, a blue-white O-type supergiant lying around 1400 light years distant. The absolute magnitude is around -6.0, indicating an incredibly hot and luminous star of spectral type O4I or O5I. Zeta is a relatively rare star indeed and has a radius 20 times that of our Sun and a mass in the range of 50 solar masses. Zeta shines around 1 million times brighter than our Sun. It therefore has a short lifespan of 3-4 million years compared to the Sun's 10 billion or so. A fierce stellar wind of around 2300 km/s ejects one millionth of a solar mass each year. Surrounding this whole area is the Gum Nebula, a vast expanse of very faint gas formed by a supernova around 1 million years ago.

Next we’ll look at v¹ and v², a blue-white B-type pair of magnitudes 4.7 and 5. They lie only 26’ north-northeast of pi, an orange K5 type giant of magnitude 2.8. In binoculars, the colour contrast between the orange and blue-white stars is rather lovely.

Sigma shines at magnitude 3.3, a sleeping giant in the sky. When a telescope is turned upon sigma, it comes alive. There in the field is a brilliant orange K5 giant star with a white companion G5 solar type star of magnitude 8.5, both stars set in a star studded field. The companion appears white instead of its expected yellow hue merely because of contrast with the primary. For added value, the primary is a spectroscopic binary, not seen visually of course but easily imagined.

L² Puppis is a red giant semi-regular variable star lying in a rich field of stars. Discovered by B Gould in 1872, it varies from 6th magnitude at minimum to a maximum of 3rd magnitude and sometimes brighter. Its 141 day period can therefore be followed with the naked eye from a darkish sky.

Sir John Herschel discovered h4038 in 1837, an unusual colour combination of a pale yellow and a red star. They lie in a lovely field, these magnitude 5.5 and 7.5 stars separated by 27”.

Another star system worth observing is h4046, floating in a beautiful field of stars. The bright orange star of magnitude 6 has a white companion of the 8th magnitude. North of the companion lies a magnitude 9 deep red star while preceding the primary is a close pair. If the night is steady, move a few degrees northeast to spot ß454. This lovely orange jewel of magnitude 6.4 has a close companion of magnitude 8.3 and the surrounding field is strewn with stars.

There is one galaxy bright enough to be seen from dark skies as it lies away from the Milky Way. NGC 2310 is a spiral of magnitude 12.8 seen edge-on. It is fairly large and can be found northeast of nu Puppis.

Of the planetary nebulae available, three stand out. The first is NGC 2440, a small bright nebula with a bluish hue. As its size is around 20”, use a high power to pull this one in. NGC 2452 is also 20” in diameter and appears small and bright in a 30cm telescope. In the same low power field is the open cluster NGC 2453, a small fan shape with 4 bright stars and many 11th magnitude and fainter.

NGC 2438 is the other planetary nebula and the best in Puppis. First find the open cluster M46 containing 150 stars from 9th to 13th magnitude. The true stellar population of this cluster may reach upwards of 500. The brightest stars are blue giants of type A and have a luminosity of some 100 Suns. On the northern edge lies a small round hazy glow. Using high power reveals a beautiful smoke ring surrounded by many stars, a truly superb sight. It was once thought to be associated with the cluster but modern studies show it as a foreground object only.

Sir William Herschel discovered NGC 2467 in 1784. A large gaseous nebula that lies in a beautiful field, it appears as a bright round haze with many stars involved. Larger apertures in the 40cm range show it as similar to the ring-like planetary nebulae though it is definitely gaseous.

There is one globular cluster, NGC 2298 a few degrees south of Canis Major. This small fairly compact cluster has a brighter central region but the outer regions are resolved only in larger apertures.

Puppis is rich in open clusters, there being around forty or so within its borders. One of the best is NGC 2477, around 2.5º northwest of zeta. Suitable for binoculars, this stunning group has around 300 members of 11th magnitude and fainter in a 20’ diameter. The centre is a lot denser and many of the stars are in curving lines.

NGC 2451 lies 1º northwest of NGC 2477. This large scattered cluster contains 50 or so bright stars centred on the magnitude 3.6 orange supergiant c Puppis.

Northwest of xi Puppis lies the open cluster M93, discovered by Messier in 1781. A beautiful group of 50 stars from magnitude 8 to 13, many of them are in groups, pairs and triplets.

Near the northern border with Monoceros is M47, nearby to M46 mentioned earlier. Messier spied this one in 1771, a beautiful cluster of scattered stars, large and rich with the brightest being a B2 type giant and the others B and A types. There are also two K-type orange giants. A double star struve 1121 lies near the centre and its magnitude 7 and 7.5 stars are easily resolved. Another star system Struve 1120 can be seen, its magnitude 6 and 9.5 components also easily separated.

Clear skies and good hunting ~ CosMos