Popular Astronomy

Share to Facebook Share to Twitter Stumble It More...

2011 Orionids

Here is Alastair McBeath's analysis of the 2011 Orionids :

The latest IMO video meteor analysis of the shower in 2011 (given as part of the October review in the February 2012 issue of the journal "WGN", 40:1, pp. 41-47, especially pp. 43 & 46) indicated the video peak was observed on the European night of October 23-24, although activity then was only marginally better than on several previous nights, beginning around October 20-21. This sort of protracted, if variable, maximum is relatively common for the Orionids, albeit the stronger peak happening as late as October 23-24 is unusual. The Organization's preliminary visual data, now updated but still available online at the address given in my October 24 posting above, suggested shower ZHRs were averaging roughly 25 ± 5 between October 20-21 and 23-24, coincident with the video findings, although the marginally highest ZHR, circa 33 ± 3 had occurred on October 21-22. This was based on relatively few reports, however.

Scarcely any UK observers had much luck in seeing the shower, and although valuable support came from the Section's overseas contributors, notably in North America and Germany, there was too little data overall to confirm or improve upon the IMO's visual findings. Unhappily, the radio meteor observers, who don't have to worry about cloudy skies, struggled at times with interference across the expected best from the Orionids, which created some rather patchy results at times. Even so, it's been possible to carry out a reasonably useful analysis of such radio data as was collected by the SPA. As quite often happens with this shower, the rise and fall from the radio maximum was relatively gradual, though the fall seemed more marked than the risen this time. Orionid activity was apparently present at fairly similar levels on October 21-22, 22-23 and 24-25, with a curious drop almost to the pre-peak level on October 23-24. Most datasets seemed to favour October 24-25 as producing the strongest response. However, as with both the IMO video and visual reports, the difference to the other better nights was small.

Overall, a peak in Orionid activity from October 20-21 to 24-25 can be suggested from all this. The difference in when the somewhat higher activity was detected by the visual, video and radio results might be due to a degree of mass-sorting within the stream, since video is able to detect meteors somewhat fainter than visual observers can achieve, and radio meteors fainter still. Such a suggestion could only be very tentative though, given the uncertainties in the individual sets of results, and especially so given the odd drop in radio rates on October 23-24. All three datasets indicated Orionid activity near the maximum was probably close to the expected value, at least. 

A list of observers whose results contributed to the SPA's Orionid files were as follows, including reports sent in directly, posted here or on the Orionids topic of the UK Weather World's Space Weather Forum can be found at : forum.popastro.com/viewtopic.php

Added by:  Tracie Heywood