The Steavenson Award


Meteor Review 2002-3

Mr Bone started by summarising the results obtained from the 2002 August Perseid shower. Despite poor weather shortly before the shower, and fears that it might join the long list of recent meteor events which had been washed out, the sky cleared up a great deal shortly before the peak. A collaboration with the BBCi science/space website had allowed the Section to encourage members of the public to perform simple measurements. Whilst none of these were of great scientific interest, they had generated public interest.

During the period August 1-2 until August 15-16, the Association had records of a total of 2216 Perseid meteors, 249 Sporadics and 103 others. The rate had taken off sharply on August 10, with the peak on August 12-13, before sharply declining shortly after 15th. The maximum zenith hourly rate (ZHR) had been of order one meteor per minute. This was comparable with the rate which had been observed fairly consistently since the 1980s. The required data analysis had been minimal: results were pooled into hourly bins, before being normalised to give the ZHR. This normalisation took account of the effect that the height of the radiant in the sky would have had upon the observed rate due to the variation in seeing conditions. The ZHR was the rate which would have been observed had the radiant been at the zenith.

The magnitude distribution was estimated by binning observations into one-magnitude sized categories. Comparison with similar treatment for sporadic events revealed that the average brightness of the Perseids, +1.8 (sample size 2216), was brighter than that of sporadics, +2.6. A consistent shift in the brightness distribution by around one magnitude was clearly discernable. There was also a marked contrast in the proportion of events recorded as leaving persistent ionisation trials: 21% of Perseids as compared to 9% of sporadics. Particularly notable had been an event at August 13 22:01UT, recorded at mag –8, and still visible two minutes later. During that time, the trail had appeared to kink and distort in the high winds of the upper atmosphere.

The Perseids are frequently reputed to be fine photographic candidates, and this claim was perhaps backed by a superb image by Worthing Astronomical Society at August 13 22:27UT. A long trail was visible with a bright flare towards one end. The same event had also been recorded elsewhere, allowing the altitude of the trail to be triangulated by studying its relative position at different observing sites. Such treatment yielded an estimated altitude of 90-92km.

Mr Bone opened his discussion of the 2002 Leonid storm with the Asher & McNaught prior forecasts. In recent years these had become renown for their accuracy, and on this occasion they were as reliable as ever. Two peaks had been anticipated, one at November 19 03:53UT resulting from the debris of the 1766 return of Temple-Tuttle, and a second peak at November 19 10:36UT as the Earth passed through the 1866 debris. The former peak was expected to give a rate of around ZHR 3000 and the latter ZHR 5000. The observations matched this predicted profile closely, and had an average brightness of mag +1.2 (based upon 455 observations). Particularly distinguished among the BAA results was Hazel McGee's image from Guildford of a bright trail at November 19 04:09UT.

Finally, Mr Bone closed with a discussion of the 2003 Quadrantid results from January 3-4. A peak had been anticipated at 22:00UT, but in the event the temporal profile had been rather flat and the rate had not been particularly high. In some years a peak rate of around 120 ZHR had been recorded, but on this occasion the maximum had only been a disappointing 40-50ZHR.

The President proceeded to introduce Roger Pickard, who would present the second short talk on the work of the Variable Star Section.






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