12:23pm Saturday 30th January 2010
By Stephen Lewis
THE 4½ inch equatorial telescope in the York Observatory is a thing of beauty. Made by Thomas Cooke of York in 1850, the exquisite brass fittings bear the hallmark of top-class craftsmanship.
Sadly, tonight, there is nothing for it to look at. There is no point even opening the observatory’s wooden dome to peer up at the night sky because all there is to see is a leaden layer of cloud, stained yellow by the city’s lights.
“We would have been looking at the moon tonight had it been clear,” says Martin Lunn, the Curator of Astronomy at the Yorkshire Museum. His small audience sighs with frustration.
Nevertheless, if you are interested in the night sky, Martin is a great person to spend a couple of hours with.
He’s a fund of weird and wonderful knowledge about the heavens, which he sprinkles into his conversation as if deliberately fishing for a reaction.
Space looks curved, he says, as we stand beside the telescope in the observatory’s dome: but of course it is not – it just seems that way because we ourselves are standing on the surface of a sphere.
Nevertheless, if a telescope wants to track a star as it swings across the heavens, it needs to move in a curve – which is why observatories have domes.
Our own star, the sun, is a comparatively small yellow dwarf. “If you were to put a giant star where the sun is, everything out to Mars would be inside.”
And, just as the village chief in the Asterix books used to fear, there really is a chance that one day, the sky will fall on our heads.
There is, swinging in orbit around the sun, an asteroid known as Apophis. On Friday April 13, 2029, there is a 25,000:1 chance that, as it swings close by the earth, its orbit will suffer a minute deflection. “And if that happens, seven years later it will hit earth.”
The chances are pretty remote, Martin admits, but if it does happen it could be apocalyptic. Apophis is about 1,000 feet across. Depending on where it landed, and the angle at which it hit, it could destroy thousands of square kilometres of land, or cause tsunamis as high as a ten-storey building. “It would do some serious damage,” Martin says.
But enough of the scaremongering.
Martin has come along to the observatory at seven on a Monday evening in January to give an introductory talk on astronomy, as part of the York Museums Trust’s ongoing series of public lectures and events.
He whips us through an account of the major constellations, and explains why many stars – such as rigel, betelgeuse and aldebaran – have Arabic names (it is because the Arab peoples who kept the flame of learning alight in the Mediterranean during the dark ages discovered the old Greek star charts, and transferred their own names on to them).
Then he shows us timelapse photographs of the night sky, which show clearly how the stars swing around the heavens during the course of the night.
“Though of course it isn’t actually the stars rotating around the sky, the effect is caused by the earth rotating on its axis,” he says.
What is of most interest to beginner astronomers, of course – apart from gazing at the moon – is trying to find the planets.
The word comes from the Greek for ‘wanderers’ – and there is good reason for that. While the relative positions of the stars appears fixed, the planets wander about the night sky seemingly at random.
Actually, the stars are moving too, Martin says – but they are so very far that we don’t notice it. “It would take 60,000, 70,000 or 80,000 years for us to notice any major difference.”
The planets, however, being fellow travellers in our own solar system, are much closer – so seem to move relative to the unchanging backdrop of the stars.
It is like seeing a swallow flit across in front of the bedroom window, while a jet plane crawls across the sky in the background, Martin says. The jet is travelling much faster than the bird – but, because it is so much farther away, doesn’t seem to be.
The wandering behaviour of the planets makes them difficult for amateurs to keep track. But there are websites that will help, Martin says, including one of his favourites, Heavens Above.
Go on there, and you will find a real-time map of the heavens above, showing all the major constellations. Highlighted in red is the exact position of the planets that are in the sky at the moment. You can even fast forward to any time you like in the future – so you know where they will be when you have time to do a bit of star gazing.
Most modern telescopes have inbuilt computers so that, once you have set them up properly, they will be able to track the planets for you, Martin says.
But they are expensive – and you still need to know how to use them properly. So his advice is: if you fancy a bit of star-gazing, go along to a meeting of your local astronomy society first.
They are full of friendly, enthusiastic people who will be more than happy to help beginners, and even advise on what telescopes to get, he says.
Sounds like a must.
• If you are interested in finding out more about the night sky, why not go along to the next meeting of the York Astronomical Society.
The society meets at the Priory Street Centre in York on the first and third Friday of each month.
It also holds regular ‘star parties’ on Knavesmire, where members and visitors can do some serious star-gazing using the society’s telescopes. The next public star party is on Knavesmire from 7pm to 9pm on Wednesday February 24, weather permitting.
To find out more about the society, visit yorkastro.org.uk
The Heavens Above website recommended by Martin Lunn is at heavens-above.com
© Copyright 2001-2012 Newsquest Media Group
http://www.yorkpress.co.uk/trade_directory/