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In pleasant contrast with the virtual washout a year previously, weather conditions for the core part of the Perseids in 2005 were reasonably favourable. Best skies were found in the southern UK, where some fortunate observers managed to put in productive meteor watches on seven consecutive nights from August 6-7 to 12-13 inclusive. The fine weather broke to cloud and rain on Aug 13-14, which at this writing is the only night for which the BAA Meteor Section lacks coverage during the most active parts of this year’s Perseid return. Clear skies were back for Aug 14-15 and 15-16, after which the waxing gibbous Moon, setting late in the night, became too intrusive to allow continued observations of the Perseids’ decline.
As of 2005 August 25, 30 sets of reports totalling 132h48m observing time had been received from those listed below:
G Beadle, G Bone, N Bone, P Brierley, A Burns, A Drummond, P Dyson, A Farr, D Gavine, M Green, A Heath, M Hurn, R Johnson, J Lancashire, T Lloyd Evans, H McGee, T Markham, B Mizon, J Randall, I Ransom, I Ridpath, G Spalding, C Steele, M Taylor, J Weightman, A White, V White, I Wood, Basingstoke AS, Worthing AS
A total of 1966 meteors (448 sporadics, 1300 Perseids, 58 others) has been reported so far.
Preliminary analysis has been undertaken to determine Zenithal Hourly Rates (ZHR) for the 2005 Perseids, making allowance for the angular elevation of the radiant above the horizon, and sky transparency. Results are summarised in the rates curve:
Perseid activity was already noticeable by Aug 6-7, with observed rates up to 5 meteors/hr corresponding to ZHR ca. 10-16. By Aug 10-11, a marked increase in activity was evident, ZHR climbing towards the mid-20s.
Peak was expected around 13h UT on August 12 - during daylight for UK-based observers. Activity was certainly climbing late on the Thursday-Friday of Aug 11-12, with ZHR 60-70 towards dawn. Immediately following the peak, rates on Aug 12-13 were again high - ZHR about 70 in the hours around midnight UT. Late on in the night, activity appears to have declined somewhat, ZHR dropping towards 40.
Fewer data are available for Aug 14-15, but it appears that by then ZHR was falling off towards the 20s, and lower still on Aug 15-16 as the usual rapid decline set in.
Overall, rates give the impression of a fairly 'normal' Perseid return. Some reports on the websites of the American ‘glossies’ suggest observer disappointment with the rates, but a measured analysis shows that these were comparable with most years in the 1980s, say, and with the well-observed 2002 return: perhaps some expectations were artificially high in recollection of the enhanced Perseid returns of the early 1990s around the perihelion of the parent comet (109P/Swift-Tuttle)?
Magnitude data for 336 sporadics and 939 Perseid meteors are summarised in the histogram below:
As usual, the Perseids showed an increased proportional abundance of bright events, and depletion at the fainter end of the magnitude range, relative to the sporadic background. Overall mean Perseid magnitude was +1.88 compared with +2.56 for sporadics in the same time interval - values, and a difference, typical of recent past years. The respective values on Aug 12-13 - the night of highest activity over the UK - were +1.77 and +2.61.
Persistent trains were left behind by 24.1% of Perseids, 4.8% of sporadics - again, pretty much in keeping with proportions seen in most years.
Alex Pratt (Leeds) and Len Entwisle (Elland) again ran video cameras in the hope of recording two-station meteors; Richard Sargent (Chester) also collaborated on this work. Early reports suggest numerous trails were captured for later analysis. Low light video exposures were also carried out by Steven Evans and Andrew Elliott. Several photographers were also active. James Weightman is among those who captured Perseids on digital camera.
Reports continue to arrive in large numbers at the time of writing, and a full formal analysis will be carried out in a few months' time once everyone has had the chance to submit their observations. Any outstanding reports will, of course, be welcomed by the Meteor Section. Many thanks to all observers for their efforts and prompt submission of results.
Neil Bone
26th August 2005 |
