Astronomy: “ An Lár ” Liam Gavin
Map shows night sky, as it appears looking roughly in the direction of Swords, at 8 pm on the 1st October. Jupiter and Saturn (just sneaking into the picture on the far left) are easy reference points (shown massively enlarged in this picture)
In ancient times, when the editor was a boy, there was a mysterious destination called “ An Lár ” that used to be displayed on some buses. It was supposed to mean “ City Centre ”, though the actual location was always in some doubt. Our Milky Way Galaxy, which contains the Sun, Earth, all the planets, comets, and asteroids, every star you can see, and another 4 or 5 hundred billion stars, has it ’ s own “ An Lár ”. As the crow flies, Dublin ’ s An Lár is around 25 Km away, but if the same crow, flying from Rush, carried on in much the same direction for another 25 - 29 light years, it would (apart from being exhausted, and very very old), reach the Galactic Centre, the “ An Lár ” of our own Milky Way. If you look in the general direction of Dublin, any dark starry night during October, you can ’ t fail to spot the giant planet Jupiter, with the not - quite - so - giant Saturn just to it ’ s left, low in the south western sky.
27 In the false colour image on the right, the location of the black hole is shown by the bright white dot in the middle, though of course in million times as massive as the Sun. It is so massive that it sucks in any stars that venture too close, sending them into a spiral descent of ever decreasing circles, until they disappear forever to feed the monster at the centre of the galaxy. They are passing through the relatively unimpressive constellation of Saggitarius, but although this constellation looks pretty nondescript, it is the location for the very centre of the Milky Way. The bright lights of Swords mean that you won ’ t be able to make out the faintly glowing Milky Way, but if you allow your eyes to follow the line from Saturn, past Jupiter, and on to the area marked by the circle on the image above, that is the very centre of our galaxy. This area contains a massive, compact object, called Saggitarius A* (pronounced Saggitarius A Star). It is a black hole, around 4.5
true colour you can never see the actual black hole, because, well, because it ’ s black of course. For years, astronomers theorised about the existence of a black hole at the middle of the galaxy, but by using the latest generation of telescopes, including the Hubble Space Telescope, a number of stars have been observed to be rapidly rotating around a point in space, and moving closer to that point with every orbit. That point is Saggitarius A*, otherwise known as the “ An Lár ” of the Milky Way, and thanks to the fortuitous position of Jupiter and Saturn this month, you now know exactly where it is.
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