Puppis, the Stern is a wholly southern constellation lying between Canis Major and Columba to its west, Hydra, Pyxis and Vela to the east, Carina to the south and Monoceros to its north. Its most prominent stars are of second magnitude and it is seen at its highest in the Southern Hemisphere's summer months. From the northern latitudes of the British Isles, only the northernmost part of the constellation rises above the horizon and is best seen during the winter months. It is relatively easily located from the close proximity of Sirius, the brightest star in the sky, which lies just a few degrees north-west of its boundary.

Mythology and History

Puppis¹ is part of a one-time giant constellation, Argo Navis, the ship Argo. Argo Navis was one of the 48 constellations listed in Ptolemy's star catalogue the Almagest. It is also the only one of Ptolemy's constellations not to be accepted as a constellation in its own right by the IAU² when they formalised specific boundaries to 88 constellations covering the whole celestial globe in 1930. The complete Argo was so large that to make it more manageable conventional reference to individual stars as being in 'the sail', 'the keel' or 'the stern'. When the IAU delineated the boundaries of the constellations they created four new constellations out of the old. These are now recognised as Carina the Keel³, Vela the Sail, Pyxis the Compass, and Puppis.

This four-way split created the anomolous situation with most of the other constellations whereby the brightest star in the constellation is given the Greek letter alpha, the next brightest beta, followed by gamma and so on through the complete Greek alphabet⁴. The split did not take into account the positions of the graded stars, so we now have, for example, alpha and beta in Carina, gamma and delta in Vela and the others spread around those two and Puppis.

In Greek mythology Argo Navis is the ship that was built by Argo for the celebrated Jason and his 50 Argonauts. The tale tells the adventures of the Argonauts and how they undertook a quest to retrieve the golden fleece of Aries the Ram from Colchis. Other stories link Argo with the boat that carries Isis and Osiris in Egyptian myth, while Christian bibliology links it with Noah and his ark, and the great deluge.

Principal Stars

Zeta Puppis is the brightest star in Puppis at +2.20 magnitude.
Rho Puppis is a variable star which dims slightly every 3.35 hours.
Xi Puppis is a giant G-class supergiant star which has an actual luminosity some 6,000 times that of our own Sun. Being 650 light-years distant it only shows at a magnitude of +3.35

Star Clusters and Nebulae

The Milky Way passes diagonally through the centre of Puppis, with the result that there are many fine star clusters to be seen, three of which are listed in the Messier catalogue. M46 and M47 are close together at the northern end of the constellation and with binoculars can be seen together in the same field of view. All three clusters are naked eye objects and appear as fuzzy patches, but can be resolved into individual stars with binoculars or small telescopes.

M46 is a rich open cluster of about 150 stars and just to its north is NGC 2438, a planetary nebula, the remains of a nova which in a larger telescope appears to be overlaying M46. In fact NGC 2438 is much closer to the Earth and is not associated with M46. It is simply a line-of-sight effect which gives an unusual 3D effect when seen together. M47 is a loose open cluster of about 75 stars of which four in a rhomboid shape are the most prominent. M93 is one of the southernmost of Messier's objects and lies about nine degrees directly south of M46 and M47. It appears as a loose irregular cluster of about 30 stars.

The Gum Nebula is an ancient supernova remnant discovered by astronomer Colin S Gum and named after him. Even by supernova standards this must have been something quite spectacular. Estimated to have occurred about a million years ago, anyone watching in prehistoric times would have been treated to a flaring orb larger and brighter than the Moon. Residue of this supernova has expanded over time to cover a massive angular size of more than 40 degrees, making it the largest nebula of its type that can be seen from Earth.

Consider that the full moon has an angular measurement of half a degree and this will give an indication of the massive displacement of this nebula. Mainly centred within Vela, the nebula spills over into Puppis. Viewed from Earth the front of the nebula is some 450 light-years away, while the rear face is all of 1,500 light-years distant. Unfortunately, this means that the whole thing is now so diffuse that it cannot be seen with amateur equipment and requires long time-lapse photographic exposures to be revealed.

NGC 2440 is a planetary nebula which is the ejected material of a sun-like star which is expanding outwards, and is now over a light-year in diameter. The material glows from the ultraviolet light from the central star which is one of the hottest known with a surface temperature of 200,000 Kelvin.

On 8 November, 1942 Nova Puppis erupted approximately five degrees due north of zeta Puppis and within 24 hours brightened to a magnitude of -0.30. Although it was the third brightest nova of the 20th Century it faded into obscurity almost as quickly. Described as a 'fast nova', it had dimmed within a month by some 18 magnitudes.

Meteor Shower

Three meteor streams exist with their radiant in Puppis. The Alpha Puppids occur only occasionally between 2-6 December. They produce meteors at a rate of up to six per-hour but their radiant is spread across a large area and encroaches into the neighbouring constellation of Vela. For that reason this shower is sometimes known as the Puppid-velids. The Pi Puppids are another variable shower which do not occur each year but when they do, their radiant is near pi Puppis and the maximum rate of four per hour occurs between 18-25 April. The Zeta Puppids are a weak shower whose maximum of three per hour occur in mid November.

Extrasolar Planets

Several stars within Puppis have been found to have single or multiple planets in orbit around them. HD 50499 has one candidate planet 1.71 times the mass of our own Jupiter. It orbits its sun in a period of just over seven years. NGC 2423-3b is over ten times Jupiter's mass and completes an orbit every two years. Both of these are gas giants but unusually their orbital periods are measured in years rather than days.

HD 69839 has no fewer than three candidate extrasolar planets. All three measure between 0.033 and 0.058 of Jupiter's mass making them closer to Earth's size than the predominant gas giants usually found. Planets HD 69830-b and HD 69830-c are close in to their parent star, but HD 69830-d revolves further out in a much more reasonable 197 days. HD 70642 b is another gas giant at almost twice Jupiter's mass but revolving around its star in 5.60 years.