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Ursids 2011

Posted: Fri Dec 16, 2011 9:38 am
by Alastair McBeath
Ending the spell of moonlit shower maxima during the second half of this year, we're now approaching the moonless Ursid peak next week. Two possible maxima are predicted, both on December 22-23, around 16h UT, and near 02h. Zenithal Hourly Rates (ZHRs) for either are expected to be between ~10-15.

However, best Ursid ZHRs can be quite variable, from ~10-50+, with especially good activity last in 1986. Theoretical work has suggested some enhancements occur about six years after the shower's parent comet, 8P/Tuttle, has reached perihelion (its period is currently around 13.5 years, and it was last at perihelion in late January 2008). Other enhancements have happened near years when the comet was at perihelion, although why is unclear, as the comet's orbit currently passes a little outside the Earth's.

In any case, such theoretical considerations are only a rough guide to reality, as enhanced ZHRs between ~25-40 were reported from 1988, 1994, 2000, 2006, 2007 and 2008, since the stronger 1986 return.

Whatever takes place this winter, New Moon on December 24 means ideal observing conditions for seeing it, while the radiant, near Kochab (Beta UMi) in Ursa Minor, is circumpolar from Britain, so is easily observable all night (and all day for radio workers).

Good luck, and clear skies!

Alastair McBeath,
Meteor Director, Society for Popular Astronomy.
E-mail: <> (messages under 150 kB in size only, please)

Re: Ursids 2011

Posted: Sat Jul 21, 2012 12:29 pm
by Alastair McBeath
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!

Contributing observers to this SPA Ursid overview are given below, including reports sent in directly, or forwarded from the German Arbeitskreis Meteore (in their journal "Meteoros" 15:2, 2012 February, provided by Ina Rendtel; see ), from the North American Meteor Network by Rich Taibi (see ), and from Radio Meteor Observation Bulletin 221 for 2011 December, via editor Chris Steyaert (see ). In the list, "R" means radio observations were provided and "V" visual ones.

Salvador Aguirre (Nevada, USA; V), Jeff Brower (British Columbia, Canada; R), Willy Camps (Belgium; R), Johann Coussens (Belgium; R), Gaspard De Wilde (Belgium; R), Karl-Heinz Gansel (Germany; R), Luc Gobin (Belgium; R), Peter Knol (Netherlands; R), Sven Näther (Germany; V), Mike Otte (Illinois, USA; R), Jürgen Rendtel (Germany; V), Steve Roush (Arizona, USA; R), Wayne Sanders (British Columbia, Canada; R), Ivan Sergey (Belarus; R), Andy Smith (England; R), Chris Steyaert (Belgium; R), Mikhail Svoiski (Arizona, USA; R), Istvan Tepliczky (Hungary; R), Felix Verbelen (Belgium; R).

As always, most grateful thanks go to all involved for their results and comments on the shower.

Alastair McBeath,
Assistant Meteor Director, Society for Popular Astronomy.