Brian Jones: Canes Venatici

Astronomy is the oldest of the sciences and people have been gazing at the night sky since before recorded history. But it’s only relatively recently that we have had something more than the unaided eye to help us. When Galileo first turned his telescope to the night sky in the early 17th century he witnessed sights for the first time that, up to then, had been hidden from human view.

Yet although telescopes can indeed reveal many wonders in the night sky, we can spend hours of star gazing with nothing more than the unaided eye to help us. On a clear and moonless night we can usually see up to 3,000 or so stars without optical aid. Unfortunately, due to street lighting and other forms of light pollution, many of us need to travel outside the cities and towns in order to witness a truly dark sky. Thankfully, walkers often find themselves located well away from city lights and so are able to witness dark skies as they are meant to be seen.

If you take a little time to look around the night sky you’ll notice that, amongst what at first appears to be a jumble of stars, patterns seem to emerge and the sky takes on a semblance of order. Many of these star patterns were described and charted by astronomers thousands of years ago and the star charts and maps of today contain many of the constellations devised by the ancients.

One of the most famous and easily-recognisable star patterns is the Plough, which is easily located lying low in the northern sky during November and December evenings. Shaped rather like a gigantic heavenly spoon the Plough is actually one part of a much larger constellation called Ursa Major, or the Great Bear, although the other stars in the Great Bear are all comparatively faint. The Plough itself, however – which marks the hind quarters and tail of the bear – stands out quite well.

While you’re looking at the Plough, check out the star in the middle of the Plough ‘handle’. You will see that this is actually a pair of stars comprising Mizar – the brighter of the two – and a nearby companion star, Alcor. Both Alcor and Mizar can be made out individually if you have keen eyesight and the sky is really dark and clear, but binoculars may be needed to bring the pair out well. If you have powerful binoculars, or a small telescope, you may see another, much fainter, star, forming a triangle with Alcor and Mizar. This star bears the somewhat-clumsy name of Sidus Ludovicianum and was named by the eccentric German astronomer Johann Georg Liebknecht in 1723. Spotting the star in his telescope and thinking he had discovered a new planet, he named it after his sovereign and patron the Landgrave Ludwig of Hessen-Darmstadt. The discovery was erroneous, but the name stuck!

The winter evenings are fairly chilly, but why not brave the elements and venture outside to seek out the celestial Plough? Happy stargazing!

Canes Venatici: Hunting dogs of the northern sky

The conspicuous pattern of stars forming the Plough (actually part of the much larger constellation Ursa Major, the Great Bear) is visible high in the sky during spring evenings and the group is quite unmistakable. As we have seen in previous blogs, the Plough is a useful pointer to many other star patterns, including the much-smaller constellation known as Canes Venatici.

Known to the astronomers of ancient China by the somewhat-unromantic name of Chang Chen – ‘a seat’ – and to later Arabic astronomers as Al Karb al Ibl – or ‘the Camel’s Burden’ – the tiny constellation of Canes Venatici, the Hunting Dogs, is visible as a small triangle of stars a short way below the ‘handle’ of the Plough as shown below.

The brightest star in Canes Venatici is Cor Caroli, a name which means Charles’ Heart, and which was given to the star by Edmund Halley in memory of Charles I. However, the star has the alternative name Chara and, along with Asterion, these two stars are shown on ancient charts as representing two dogs held on a leash by Bootes, the Herdsman. Bootes is depicted by a larger constellation a little way to the east (and which will be described in next month’s blog). Arcturus, shown on the chart below, is the leading star in Bootes who, with the help of Chara and Asterion, is eternally pursuing the Great Bear around the northern sky.

If you have a small telescope you might like to take a closer look at Cor Caroli which is in fact a double star. Each of these stars is white and similar in size and brightness to our own Sun. The pair shine from a distance of around 110 light years, which means that the light we see from Cor Caroli actually set off on its journey towards us around the end of the reign of Queen Victoria!

Although only tiny, the constellation Canes Venatici is notable in that it plays host to the celestial showpiece Messier 3, or M3, located on a line from Asterion through Cor Caroli and extended towards the bright star Arcturus as shown here. M3 is a member of a class of objects known to astronomers as globular clusters and, like all globular clusters, this object lies outside our Galaxy. M3 is located at a distance of well over 30,000 light years and contains around half-a-million stars compressed, as its descriptive name suggests, into a globe-shape with an actual diameter of around 200 light years.

If you have really keen eyesight, and the sky is very dark, clear and moonless, you might be able to pick out M3 with no optical aid whatsoever. However, you’re best looking for it with a pair of binoculars. When seeking out this object, and others of its type, try to look for a patch of luminosity rather than a point of light. Once you’ve found it, M3 should be visible as a tiny, spherical cloud.

It is a sobering thought that, should you manage to glimpse M3, the light you are seeing from this remote object set off on its journey towards us over six times as long ago as the age during which Stonehenge and the Great Pyramid of Giza were constructed – the universe is truly a huge place!

Now the evenings are warmer, why not try spotting the celestial hunting dogs and seeking out its remote but inspiring globular showpiece? Happy stargazing!

This entry was posted on: Friday, May 7th, 2010 at 11:02 am
Filed under: Blogs
Tags: astronomy, night-walking
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Brian Jones: Canes Venatici

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