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Village Sky At Night with Brian Watkiss

Take a long look at our ever-changing universe

Posted on May 01 2009 at 7:49:01 0 comments

Summer is almost here, as you can tell by the fact that it doesn’t get dark till gone ten o’clock. Looking south west soon after dark, Leo dominates the sky, with Saturn still obvious underneath, although Saturn is not as bright as usual this year because its rings are virtually edge on to us.

Looking at the last two stars in Leo’s tail, draw a line through them, down and left (east) for about twice the distance between them and you will come to a big, crooked diamond of stars.

This is the constellation of Virgo. The brightest star, at the bottom of the diamond, is Spica. It is a very hot blue star, or rather a pair of stars so close that you can’t separate them, about 260 light years away.

These stars are 2,000 times as bright as our sun and emit so much radiation that any planets orbiting them are highly unlikely to support life. Above the top of the diamond and just to the left is another bright star, Arcturus. This sits at the bottom of a group of six stars forming a kite shaped constellation, leaning off to the left. This is Boötes (usually pronounced like babies’ footwear). With Sirius now gone, Arcturus is the brightest star in the sky, although it appears distinctly orange in colour. Compare it to the blue-white of Spica.

It is only 36 light years away and looks orange because it has used up most of its hydrogen fuel. It is also moving very quickly, for a star, so that in half a million years it will be too far away to be visible – so get out tonight and have a look.

Because it is so close and moving so quickly, its apparent position relative to the background stars changes, a fact noticed by the astronomer Edmund Halley and made him realise that the universe is not fixed but constantly changing.

For the first few days of May, Mercury will be visible in the twilight immediately after sunset, very close to the sun. You will, however, need a very good view of the north western horizon, a really good clear sky and very good eyesight.

Early risers will be seeing Venus as the morning star, rising just before the sun but still very low in the sky. The first part of the month could also see an increase in meteors (shooting stars) as earth passes through the dusty debris left behind by Halley’s Comet.

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