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Star blotted-out by asteroid

Posted: 8 September 2014

Have you ever seen a star completely wink out, disappearing completely from view for a few seconds? On the morning of 10 September there is a great chance to see just that but the event is only visible along a narrow, 90-kilometre path across Northern Ireland and Scotland, with the cities of Glasgow and Dundee on or close to the centre of the path.

The path of the asteroid occultation cuts across central Scotland, Northern Ireland and into the Republic of Ireland, with Glasgow and Dundee near the centre line.
On 10 September at around 3.06am the star HIP 22792, shining at magnitude +7.6, will be occulted by the asteroid (569) Misa, a mag. +14.6 body with an estimated diameter of 65 kilometres. The asteroid itself is too faint to be seen in apertures under 300-mm (12-inch) but the startling effect it will have on the star will be a brilliant and easy thing to see in binoculars.

Knowing the positions of the stars and the brighter, numbered minor planets to a high degree of accuracy, astronomers can calculate when an asteroid (Moon and the planets too) will move in front a star. As Misa occults HIP 22793, the star will suddenly disappear from sight for 3.6 seconds for observers with binoculars and are situated right on the centre line. The joint magnitude of the pair will fade by seven magnitudes to +14.6, the value for the asteroid and then the star will instantaneously reappear, it's magnitude 'restored' to +7.6. The star is placed in the constellation Taurus and will be 38 degrees high above the eastern horizon, well above all the murk and muck at the horizon.

Observers well placed to see this remarkable and thrilling event can just observe it for fun but such events can yield much useful science, with it entirely possible to determine the size and shape of the asteroid, in this case Misa. This is achieved by accurate timings from an properly calibrated electronic stopwatch by observers spread out along the length and breadth of the predicted path.

Those located closer to the centre line will see a longer occultation, with those on the periphery experiencing an increasing shorter fade the further from the centre line they are. Some observers right on the edge of the track may see no fade at all, but such negative results are just as valuable as they help to pin down Misa's dimensions. For more information check out:

This event will is ideal for astronomical societies to attend and maybe pool resources if the aim is to do some science. Check out the FAS website.

The path of the occultation runs south-west to north-east across north-western Ireland, most of Northern Ireland and mid-Scotland. Astronomy Now expert Peter Grego reports on the path:

"Beginning in the west, the central line makes landfall at the Mayo coast, runs just north of Westport and proceeds through Sligo; across the border it continues right through the middle of Strabane and across all five northern coastal counties of Northern Ireland, leaving the coast just north of Ballycastle. After crossing the North Channel it runs across southern Kintyre and northern Arran, over the Firth of Clyde to Largs, then clips northern Glasgow and Stirling, southern Perth and northern Dundee, finally leaving the east coast at Montrose."

Let's hope for clear skies on the morning of 10 September and enjoy this rare and exciting event, whichever way you decide to observe it.