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Village Sky At Night with Brian Watkiss

Plough a path to Polaris – our friend in the north

Posted on April 01 2009 at 7:53:14 0 comments

The beginning of March brought us the comet Lulin, which was predicted to be just visible with the naked eye. Well, I don’t think it ever reached that brightness, even with dark, clear skies; and nowhere near in the light-polluted sky over Alvechurch. It was just visible through binoculars and I managed to grab a photo of sorts (below) but then comets are notoriously unpredictable.

Now, we have seen Venus as the Evening Star and Sirius the Dog Star is starting to disappear; but there is another “named” star which is the most useful star in the sky. This is Polaris or the North Star, useful because it always sits above the North Pole.

It is very easy to find by first finding the Plough, not a constellation but an asterism, which just means a pattern of stars, usually part of a recognised constellation. This is the famous “saucepan” pattern, at the moment overhead, with the handle pointing east.

The top two stars, on the side away from the handle, are Merak on the right and Dubhe on the left. Merak is similar to our Sun, about 80 light years away, whereas Dubhe (made famous by Frank Sinatra) is a red giant, nearly 60 times as big as our sun and 127 light years away.
Drawing a line from Merak through Dubhe and leftwards for about six times that distance, you should arrive at a star of very similar brightness. This is Polaris, another red giant, very similar to Dubhe but over 400 light years away. It has two smaller stars orbiting round it but you can’t separate these with the naked eye.

At the moment it is very close to the pole but not quite over it, and as time goes by and the Earth’s axis wobbles round the sky, it will move further away from North. This “wobble” is called the Precession of the Equinoxes and means that in 12,000 years’ time, Vega, very low in the north east at the moment, will be the North Star.

Now you are facing north, if you turn around, it follows that you will be facing south. But – note that east is now on your left and west on the right. Obvious, but can cause confusion when looking at star charts or a planisphere. So, looking slightly to the east of south, early in the evening, is the lovely sight of Saturn, just below Leo.

If you look out for Saturn on every clear evening, you can watch it drift westwards as the weeks pass and really get a sense of how the Earth orbits the Sun much more quickly. Leo is still dominating this part of the sky and to the southwest is Gemini, the twins.

Below the head of Gemini and slightly east is Procyon, which, together with a smaller star just to the west, forms the constellation Canis Minor – the Little Dog. To me, two stars just form a straight line, but see what you think.


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