Some years ago, this feature discussed the various cat constellations that are scattered around the sky. It would only be fair, then, for their canine counterparts to have their turn as well, since there are several dog constellations throughout the heavens.
Perhaps it is fitting that this is the case since, after all, the first animal to travel in space was a dog. This was Laika, a stray dog from the streets of Moscow, who flew aboard the second satellite ever launched into orbit, Sputnik 2, on Nov. 3, 1957. Measurements of several of Laika’s vital signs were made during the first few orbits, but it appears she died from overheating a few hours after launch.
The most prominent of the dog constellations rides high in our southern sky throughout the evening hours of these chilly mid-February nights. This is Canis Major, the big dog. By far Canis Major’s most eye-catching feature is the bright star Sirius – generally taken to mark the dog’s eye – which happens to be the brightest star in the entire nighttime sky.
Sirius is often referred to as the Dog Star due to its location and prominence within Canis Major. During the northern hemisphere’s late summer, Sirius rises at approximately the same time as the sun, and – so it could be imagined – its light and heat is added to that of the sun. Thus, the expression “the dog days of summer.”
Sirius is about twice as massive as our sun, and about 1.7 times the sun’s diameter. But what really makes Sirius so prominent in our nighttime sky is its proximity to our solar system: it lies only 8.6 light-years away, the second-closest of all the naked-eye stars, and the seventh-closest of all known stars. Sirius is, for the time being, approaching our solar system, and will be closest, 7.8 light-years, some 60,000 years from now; it will then begin receding from us, but will remain the brightest star in our nighttime sky for another 150,000years.
In the mid-19th century the German astronomer Friedrich Bessel deduced that Sirius was accompanied by an unseen companion. In 1862 an American telescope-maker, Alvin Clark, first observed this companion, and we now know that this object is a white dwarf, i.e., the remnant core of a star that has gone through its life cycle and shed its outer atmosphere – something our sun will become in a few billion years’ time. Sirius and its companion orbit each other every 50 years, and for the next few years they will be as widely separated as they can be – and thus it will be possible to detect the companion with larger backyard telescopes.
Canis Major contains much more than just Sirius, of course. The dog’s hindquarters are marked by a triangle of moderately bright stars; the brightest of these, known as Adhara, appeared almost as bright as the planet Venus in our sky when it was relatively close to our solar system five million years ago, and would still be the brightest star in our nighttime sky if our eyes were sensitive to ultraviolet light.
The Milky Way travels through Canis Major, and thus sky-watchers armed with small telescopes can find various star clusters and clouds of gas and dust scattered throughout the constellation. About a decade and a half ago some astronomers pointed out evidence that suggests a background dwarf galaxy lies hidden behind the dust and gas of Canis Major, but this evidence is not regarded as conclusive at this time.
To the north and east of Canis Major is another dog constellation: Canis Minor, the little dog. There are few naked-eye stars within Canis Minor, but one of these is Procyon, the eighth-brightest star in the nighttime sky. Procyon is also close to our solar system, being 11.5 light-years away, and, like Sirius, has a white dwarf companion. Sirius, Procyon, and the bright star Betelgeuse in Orion form a large equilateral triangle, often referred to as the Winter Triangle.
We have to wait until an hour or two before midnight before we encounter another dog constellation: this is Canes Venatici, the hunting dogs, located south of the Big Dipper’s handle. There is one moderately bright star in Canes Venatici: Cor Caroli, Charles’ Heart, in reference to either King Charles I or Charles II of England. There is evidence that supports either monarch. When we look toward Canes Venatici we are looking away from the plane of our galaxy and out into intergalactic space, and there are several moderately bright galaxies that are detectable with decent backyard telescopes.
The two remaining dog constellations are both located within the northern hemisphere’s summertime Milky Way. Vulpecula, the fox, is a relatively small constellation located south of the prominent constellation of Cygnus, the swan. There aren’t any prominent naked-eye stars within Vulpecula, but small telescopes can detect what is called the Dumbbell Nebula, a bright example of what is called a planetary nebula – the expelled atmosphere of what used to be a normal star. In the far future, our sun’s atmosphere will appear as a planetary nebula before it disperses into space and leaves the white dwarf behind.
To the south and west of the prominent constellation Scorpius is Lupus, the wolf. There are several moderately bright stars in Lupus, most of these being members of a loose association of hot young stars that also includes several of the stars of Scorpius. The brightest star in Lupus, however, appeared over a millennium ago: this was a brilliant supernova that appeared in the year 1006, which was widely reported as being visible in daytime, and which is apparently the brightest supernova that has appeared within historical times. Despite being located over 7,000 light-years away from us, the gamma-rays from this supernova contributed to the production of nitrates within the ice of Antarctica – showing that even cosmic dogs can leave a bite.
Alan Hale is a professional astronomer who resides in Cloudcroft. Hale is involved in various space-related research and educational activities throughout New Mexico and elsewhere.