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Brian Jones: Celestial guides

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!

Brian

Along with its larger relative, the Little Bear (or Ursa Minor) is one of the oldest depicted star patterns and appears in a catalogue of constellations compiled during the second century BC by the Greek astronomer Ptolemy. Visible high in the northern sky as seen from mid-northern latitudes, the Little Bear is easily found by using the two end stars in the ‘bowl’ of the Plough as pointers, as shown below. Just follow a line from Merak through Dubhe you will reach the star Polaris – the brightest star in Ursa Minor and the end of the Little Bear’s tail.

Although Ursa Minor isn’t the most prominent of constellations, it can be picked out fairly easily because the area around it is devoid of bright stars. It roughly resembles the Plough in shape and stretches away from Polaris, the main star in the group. Polaris, or the Pole Star, as its name suggests, marks the position of the north celestial pole. This is the imaginary point in the heavens which lies in line with the Earth’s axis, and consequently directly overhead as seen from the North Pole and in the direction of north when viewed from elsewhere on the Earth’s surface. Polaris appears to remain stationary as the Earth turns on its axis, with all the other stars appearing to go round it every 24 hours.

Ursa Minor and Pointers with Horizon

If you look at the celestial bears you will notice that they both have long tails – unlike their earthly counterparts. Of course, there is a legend to explain this. Ursa Major (the Great Bear) represents the legendary maiden Callisto – who was so beautiful that the Roman goddess Juno (wife of Jupiter, the King of the Gods) became jealous, and turned her into a bear. Years later, Callisto’s son Arcas almost killed the bear while out hunting. Jupiter then turned Arcas into a bear and, in order to save them both from Juno’s clutches, grabbed both animals by their tails and swung them high up into the sky where they can be seen to this day. Naturally, the tails of both animals became stretched in the process!

At the other end of the constellation, the stars Kochab and Pherkad are known collectively as the Guardians of the Pole. Pherkad is actually a wide double star and both stars that form this double can be seen with binoculars. The pair are white and orange-yellow, although you may need a telescope to bring the colours out properly. Kochab is also orange-yellow in colour and is one of the closest stars in Ursa Minor, its light taking just over a century to reach us.

Polaris, on the other hand, shines from a distance of 680 light years. In other words, the light we are seeing from Polaris set off towards us around the reign of Edward III. The star appears relatively faint although in reality it is around 6,000 times as luminous as our Sun and only appears faint due to the fact that it lies at such a great distance from us. So though the winter evenings are fairly chilly, keep an eye to the heavens when you’re out walking and think of the Little Bear and the Pole Star as your celestial guides. Happy stargazing!

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