2011 Ursids

Here is Alastair McBeath’s analysis of the 2011 Ursids :

Following the disappointing run of badly moonlit, and commonly badly weather-affected, meteor showers in late 2011, sadly the moonless Ursids seemed to have done no better for clearer skies, with scarcely no visual reports received by either the International Meteor Organization (IMO) or SPA. However, as the two advance possible maximum predictions noted earlier here were joined barely a day before the event by a third, suggesting peak ZHRs of ~10-15 on top of the usual activity might happen just before 18h UT on December 22, it has been important since to try to establish what may have taken place.

Data from the IMO’s video observations of the shower were discussed briefly in the Organization’s journal “WGN” 40:2 for 2012 April, pp. 69-75, especially pp. 70-71. They indicated just a single sharp peak had been found at 19h UT on December 22, with an estimated visual-ZHR-equivalent of ~15, although being based largely on European results, any events during European daytime could have been missed.

As the Ursid radiant is circumpolar for all our usual northern hemisphere radio meteor observers, located in Europe and North America primarily, it is one of those rare showers whose activity can be followed from all locations throughout the day and night, interference and other technical problems permitting! Carrying out the usual analysis of this data suggested that Ursid activity had probably been present at a radio-detectable level from roughly 02h UT on December 22 through to at least 11h UT on the 23rd. Within that time, the main shower maximum was undoubtedly in the 19:00-20:00 UT interval on the 22nd (remembering that most radio observers provide data in one-hour long recording periods only). It was surrounded by a spell of better than normal, but below-peak, rates from circa 16h-22h. Judging the strength of meteor activity purely from radio data is extremely difficult, although in this case, it was plausible the Ursid activity was fairly normal, so likely close to ZHRs of ~10-15. This was all reassuringly similar to what the IMO video data had proposed.

There appeared to have been several lesser radio maxima as well, although these were generally less convincingly recorded than the main one. Ignoring those which likely resulted solely from better radiant geometry from the two chief geographic regions, those on December 22 around 10h-12h and on December 23 around 07h UT remained as potentially interesting. Unhappily, the lack of other data meant no further investigation of these could be performed.

It remains intriguing that none of the predicted maximum timings coincided at all well with what was actually found, stressing the importance of making observations for as long as possible whenever a meteor shower peak is due, rather than relying heavily on what is “supposed” to happen!

A list of observers whose reports were used in this analysis can be found on the SPA Forum at forum.popastro.com/viewtopic.php

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