Monday, 23 July 2007


The most popular, if not the best, of the annual meteor showers is the Perseids, which will start to grace our skies soon. Maximum will be on the night of 12/13 August, but some can be seen from 23 July to 20 August. Conditions this year are good, with no moonlight to interfere on the night of maximum, and the actual time of maximum, at 03h BST on the 13th, coincides with the time when the radiant, in Northern Perseus, will be highest in the sky for observers in the UK/Ireland. In good dark sky conditions an experienced observer should see an average rate of about 80 per hour at around that time.
But beware of some uninformed predictions! Just because the shower 'starts' on 23 July, and has a quoted rate of about 80/hour, does NOT mean that you'll see lots of meteors from 23 July onwards! A meteor shower is defined as beginning when the rate of meteors from that shower rises above 1/4 of the normal background sporadic meteor rate. In other words, when about 1 in 4 of every meteor seen is a member of that shower. Since there are about 10-12 sporadic meteors per hour visible in good conditions at this time of year, that means that you might see about 3 Perseid meteors per hour on July 23. (The converse applies to define the end of a shower).
So, like all meteor showers, the level of activity starts slowly, and gradually builds up to the peak. You won't see a significant number of Perseids until near the end of the first week in August. However, it IS worth looking any time from early August onwards.
The IAA will be holding a special 'Perseids BBQ' on the evening of 12-13 August, weather permitting. More details on that soon.

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