Constellations: Overview | Andromeda | Antlia | Apus | Aquarius | Aquila | Ara | Aries | Auriga | Boötes | Caelum
Camelopardalis | Cancer | Canes Venatici | Canis Major | Canis Minor | Capricornus | Carina | Cassiopeia | Centaurus
Cepheus | Cetus | Chamæleon | Circinus | Columba | Coma Berenices | Corona Australis | Corona Borealis | Corvus
Crater | Crux | Cygnus | Delphinus | Dorado | Draco | Equuleus | Eridanus | Fornax | Gemini | Grus | Hercules | Horologium
Hydra | Hydrus | Indus | Lacerta | Leo | Leo Minor | Lepus | Libra | Lupus | Lynx | Lyra | Mensa | Microscopium | Monoceros
Musca | Norma | Octans | Ophiuchus | Orion | Pavo | Pegasus | Perseus | Phoenix | Pictor | Pisces | Piscis Austrinus
Puppis | Pyxis | Reticulum | Sagitta | Sagittarius | Scorpius | Sculptor | Scutum | Serpens | Sextans | Taurus
Telescopium | Triangulum | Triangulum Australe | Tucana | Ursa Major | Ursa Minor | Vela | Virgo | Volans | Vulpecula

He is your friend, your partner, your defender, your dog. You are his life, his love, his leader. He will be yours, faithful and true, to the last beat of his heart. You owe it to him to be worthy of such devotion.
– Anonymous

Canis Major the Constellation

Canis Major was listed by Ptolemy as one of the 48 original constellations handed down from antiquity. It is 43rd in size of the 88 internationally recognised modern constellations.

Bordered by Monoceros, Lepus, Columba and Puppis, Canis Major represents the larger of Orion's two dogs. This one is right on the tail of Lepus, the hare. Canis Major is best known for containing Sirius, the 'Dog Star', which ancient mariners navigated their sailing vessels by.

There is one Messier object in Canis Major, M41 (NGC 2287), an outstanding open star cluster. It also contains HD 47536, a star with a duo-planetary solar system. Then there is the most massive star that we know of, VY Canis Majoris.

There are also two planetary nebulae, IC 2165 and Min 3-1, and the enigmatic emission nebula known as Thor's Helmet.

There is an astonishing feature beyond Canis Major: a pair of colliding galaxies, NGC 2207 and IC 2163. This is an intergalactic combination of cosmic proportions, and it is taking place on an awesome scale, both in terms of size and time.

Stars

The scientific star names are simple to understand (if you know your Greek alphabet). For example, 'alpha' means it is the brightest star in that constellation. This is known as the 'Bayer designation'. The next brightest is designated 'beta' etc, or that is the way it is supposed to work. Sometimes the stars are variable or the cataloguing was a little off, so the list has the appearance of a dog's hind leg. In this constellation we have the alpha star in the correct place, then the epsilon, followed by delta, beta, eta, omicron², zeta, sigma, kappa, omicron¹, nu², omega, theta, then gamma!

Some stars have proper names as well. For example, alpha Canis Majoris is known as Sirius. Others are known by their catalogue number.

Sirius

Sirius is actually a binary system comprising a white main sequence star, Sirius A, and a dim dwarf star, Sirius B. The apparent magnitude is −1.43, although this is variable. It is so bright because of its nearness to Earth, at 8.58 light years² distant, Sirius, known as the 'Dog Star', is the fifth-closest to us.

The ancient Egyptians used the pre-dawn (heliacal) rising of Sirius to predict the flooding of the Nile, which they called akhet (the inundation). This was essential to all life in Egypt. They even assigned a special god to oversee this action.

Along with Procyon and Betelgeuse, Sirius forms the Northern Hemisphere's Winter Triangle. Another interesting geometric asterism is the rhombus created by connecting Sirius, Rigel, Aldebaran and Betelgeuse.

VY Canis Majoris

VY Canis Majoris is a red hypergiant. At around 2,000 solar radii, it is the biggest star known to us. Scaling it next to our sun is like comparing a beachball to a pinprick. If this star were at the centre of our solar system instead of the Sun, its surface would be at the orbit of Saturn, and we would be inside it.

New General Catalogue (NGC)

The NGC was compiled by John Louis Emil Dreyer (director of the Armagh Observatory from 1882 - 1916). NGC 2362, also known as the Tau Canis Majoris Cluster, was first noted by Giovanni Hodierna in 1654. It was catalogued by William Herschel in 1783.

A fascinating feature is a post-merger duo-core galaxy, the lenticular NGC 2292 and elliptical NGC 2293. These are given separate catalogue numbers, yet they are now one complete galaxy, verging on spiral.

Thor's Helmet (NGC 2359) is a bright emission nebula with unusual properties. Astronomers suspect it is powered by a rare Wolf-Rayet star; these stars are named after their discoverers Charles Wolf and Georges Rayet. They are blue supergiants which eject stellar wind at a phenomenal speed, causing a 'bubble' effect in the nebula. The stars are massive, over 20 times the mass of our Sun. They have a high rate of mass loss, equivalent to an Earth mass per year. This shortens the star's life and will eventually cause them to go supernova.

Canis Major Dwarf Galaxy

The Canis Major Dwarf is an irregular galaxy, possibly our closest neighbour at 25,000 light years distant. Interestingly, it is 42 thousand light years from the Galactic centre. Discovered in November 2003, this galaxy is thought to contain around a billion stars. It is not in the Canis Major constellation (those stars are all in our Milky Way galaxy) - it is far beyond it. We say it is part of the constellation so that we know which direction to look and in what portion of the sky.

Extrasolar Planets in Canis Major

The nomenclature that has been decided upon for extrasolar planet discoveries is to use a lower-case letter after the parent star catalogue number (or name), eg 'HD 47536 b'. This stays with the planet even if more discoveries are made within the same solar system, and despite the position of the new planet relative to the star. Therefore, the first-discovered planet of HD 47536 is HD 47536 b, with HD 47536 c, and so on, having been detected later.

One extrasolar planetary system had been found in the constellation Canis Major up to 2007; containing two planets. The first, HD 47536 b, was discovered in 2003 and orbits within the system's 'Goldilocks Zone' (habitable range). Unfortunately, it is a gas giant and therefore not a prospect in the search for extraterrestrial life. However, if it has any rocky moons with enough gravity to sustain an atmosphere then they would be a distinct possibility. The second planet, HD 47536 c, takes almost seven years to orbit the star and, due to a lack of liquid water, life as we know it is beyond the realms of possibility.

The figures given in the table below are the length of the planet's orbital period around its parent star, which we know of as a year. The mass of the extrasolar planet is compared with that of Jupiter, our solar system's largest planet, known to astronomers as the 'Jovian scale'.

Down to Earth

Sirius Black was an important character in the 'Harry Potter' series of books by JK Rowling.

Canis Major in Science Fiction

Many science fiction authors have chosen Canis Major (and Sirius in particular) to base their adventures or write about extraterrestrials who hail from that vicinity. These writers include Lucian of Samosata (the first sci-fi writer that we know of), Douglas Adams, François-Marie Arouet, Isaac Asimov, Arthur C Clarke, Larry Niven and Eric Russell.

The sequel to 101 Dalmations is The Starlight Barking by Dodie Smith - and it involves the 'dog star' Sirius, of course! Popular TV shows also feature the Canis Major constellation stars quite heavily, eg,Star Trek, V and Doctor Who.

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¹ Current IAU guidelines use a plus sign (+) for northern constellations and a minus sign (−) for southern ones.
² A light year is the distance light travels in one year, roughly 5.88 trillion miles or 9.46 trillion km.
³ This means 114 million light years.