29-09-2007 October Night Sky (Article 105)

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Simon Kenny
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Joined: Tue Feb 12, 2008 9:17 pm
Location: Shannon, Co. Clare, Ireland

29-09-2007 October Night Sky (Article 105)

Post by Simon Kenny » Wed Feb 04, 2009 11:23 am

October Night Sky (Article 105)

“We had the sky up there, all speckled with stars, and we used to lay on our backs and look up at them and discuss whether they was made or only just happened”. So said Mark Twain’s character Huckleberry Finn. Despite its magnificence, the starry night sky can be a bewildering chaos of luminous points. All the stars are suns of different sizes, colours and distances, and it is the vast distance that makes them all seem the same. The most pleasurable way of observing celestial objects is with the mind as well as with the eye, and hence our ancestors created the constellations, joining up the brighter dots to form persons and objects from their lore and ideology. High in the south this month is one such constellation, Pegasus, the celebrated winged horse of the Greek legend of Perseus and Andromeda.

The horse is visualised flying upside down as viewed from the northern hemisphere, and its primary shape is of a Great Square and not a horse. Nor is it a true square and its conspicuousness is due in part because it encloses a very star poor area. The Sumerians, who in the 4th millennium BC created the first of the great civilisations of Mesopotamia, knew the Great Square as a field. Characters from the Perseus-Andromeda story did not appear in the Mesopotamian heavens, but the Great Square was adopted by the Egyptians within its planisphere of the Temple of Hathor at Dendera. Three lines of faint stars trailing west of the square represent the horse’s forelegs, and head.

Note the colour differences of the four corner stars, best seen in binoculars, from blue-white to reddish-orange. The top right star, Scheat, is a red giant. The Great Square is also used as a rough measure of how dark and clear your sky is. With light pollution the naked eye may see a couple of stars within the square, whereas from a really dark site one can see dozens.

Next club meeting is on Wed. 3rd Oct. at 8 pm, room 206, Mary Immaculate College when Paddy Stack from Kerry Astronomy Club will give a talk on ‘Exploration of Mars by space probe’.

On the weekend of 5th to 7th Oct. 2007 the club holds the 23rd consecutive Whirlpool Star Party (WSP) in Birr. The WSP attracts astronomers from all over the world and is a recognised major event in the international astronomy calendar. This is a relaxing and informal weekend and apart from talks by leading astronomers there is an opportunity to visit the Great Telescope in Birr Castle and, weather permitting, to have a look through some of the attendees telescopes from the Castle grounds with the kind permission of our patron, the 7th Earl of Rosse, descendant of the 3rd Earl, who built the 72” Leviathan in the 1880’s. This year we have a great line up of both Irish and international speakers.

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