Tue, 09 Aug 2016
Good year for Perseid meteors
The maximum of the annual Perseid meteor shower is due on Thursday and Friday, 11–12 August. The comparatively warm August nights make the Perseids probably the most popular meteor shower of the year, even though observed rates are not as high as the Geminids in December.
And this year, rates are likely to be somewhat higher than usual due to a 12 year periodicity in Perseid rates caused by perturbation of the meteor stream by Jupiter. This has previously enhanced Perseid rates in 1968, 1980, 1992 and 2004. Good news for observers in the UK is that predictions indicate that the enhancements will occur during UK hours of darkness. However, the SPA Meteor Section Director warns against expecting a storm of meteors, as hyped up by some media.
Meteor rates are measured by their ZHR – Zenithal Hourly Rate, which is based on ideal conditions and position of radiant. In practice, you can expect somewhat lower rates. The predicted ZHR for the Perseids, normally about 80 per hour, may increase to 150–160 for a short period. Brief outbursts may occur at about 23:34 BST on Thursday, 11 August,and also about an hour later at 00:23 BST. So the best night to watch may be the Thursday–Friday, 11–12 August, though good numbers could occur on Friday–Saturday 12–13 as well. Ideally, you should observe for at least an hour, and preferably longer.
The Moon is at first quarter on 10 August and will be a slight problem earlier in the evening of maximum, setting around midnight, but greater rates are likely after midnight in any case. The Perseids are a shower that favours those who stay up late! Peak rates in general are seen around 3 am, before it starts to get light.
What are the chances of even higher rates, as reported in some places? Tracie Heywood, SPA Meteor Section Director, writes: "There is no chance of a Perseid meteor storm, or of seeing 200 meteors per hour. We might hope to see observed meteor rates approaching double their normal level for a while (exact timing uncertain) during the night of Aug 11-12 ... but there is no guarantee of this!"
If you do miss the peak, don't give up on the Perseids. The shower is active during the first three weeks of August, though the increasing phase of the Moon will hinder observations. But dedicated observers will be able to observe for several days after maximum in the early hours.
Added by: Robin Scagell