Unfavourable lunar phasing has affected many of the major annual showers through the autumn of 2005, the Orionids, Leonids and Geminids each being notable casualties. A couple of reasonably favourable opportunities remain before meteor activity hits its annual low point during late January into February.
Ursids
Active December 17-25 Radiant RA 14h 28m Dec +78o
A much-neglected but moderately active shower, the Ursids are produced by debris from Comet 8P/Tuttle. The radiant, near the ‘dipper’ or ‘Guardians of the Pole’ in Ursa Minor, is circumpolar for observers at the latitudes of the British Isles; at the time of maximum on December 21-22, it is highest during the early morning hours – figures below are for 53oN:
Local Time Altitude Local Time Altitude
18 42.8o 01 47.5o
19 41.6o 02 50.3o
20 41.0o 03 53.4o
21 41.1o 04 56.5o
22 41.9o 05 59.5o
23 43.2o 06 62.1o
00 45.1o
Moonlight will present some problems in the later parts of the night – the Moon reaches Last Quarter on December 23. Watches in late evening should, however, still be productive.
Ursid meteors are fairly slow (atmospheric entry velocity 33 km/s), and mostly quite faint. Observed rates are usually less than 10 meteors/hr, but occasional unexpected outbursts have occurred, as in 1946, 1982 and 1986.
Quadrantids
Active January 1-6 Radiant RA 15h 28m Dec +50o
Of the major showers capable of producing strong activity, the Quadrantids present the best dependable opportunity for observers to enjoy high meteor rates until the closing months of 2006. The shower has a narrow, sharp peak during which corrected Zenithal Hourly Rate (allowing for haze and radiant elevation above the horizon) can be as high as 120 – corresponding to observed rates of one or two per minute. High activity is restricted to within about 8 hours either side of the peak; at other times, only a slow ‘trickle’ of one or two meteors/hr is evident.
In 2006, maximum is expected at Jan 3d 17h UT, early in the evening for observers in the British Isles. At this time, the shower radiant (in northern Bootes, down and to the left from the Plough’s ‘handle’ from the UK perspective) is sinking towards the northwest of the sky. Even with a relatively low, and declining, radiant elevation (see table for 53oN below), high rates could make the evening hours of Tuesday-Wednesday Jan 3-4 productive. A 4-day waxing crescent Moon shouldn’t interfere too badly, low in the western sky and setting around 20:30 local time.
Local Time Altitude Local Time Altitude
17 22.5o 00 21.8o
18 18.1o 01 27.2o
19 14.9o 02 33.3o
20 13.3o 03 41.8o
21 13.1o 04 49.0o
22 14.6o 05 56.9o
23 17.5o 06 66.3o
The Quadrantid radiant is, in fact, circumpolar from the latitudes of the British Isles, meaning that activity can be seen throughout the night. Lower culmination, due north, is reached around 21h local time, bit the radiant doesn’t really start to climb to any great elevation in the eastern sky until well after midnight, by which time rates on 2006 Jan 3-4 can be expected to be in decline.
Results in past years have shown significant particle-sorting by size with in the Quadrantid meteor stream. At the time when visual activity is highest, the majority of Quadrantids are faint (smaller material). Photographic-range meteors (magnitude 0 and brighter) become more abundant some hours after maximum. In 2006, UK-based observers will be in the ideal longitude zone on Earth to witness and record the ‘bright meteor’ phase of the Quadrantids.
Quadrantid meteors are fairly slow (atmospheric entry velocity 42 km/s), and the brighter shower members are sometimes strongly coloured (often blue or green). The stream’s dynamic orbital history – much perturbed by Jupiter’s gravity – has made identification of its parent body difficult. It has been suggested that Comet 96P/Machholz may be the source, while more recent studies have proposed that the Quadrantids may be debris from asteroid 2003EH1, a possible break-up product of Comet 1490Y1 following the latter’s close approach to Jupiter in 1650.
Poor January weather frequently limits, or completely prevents, Quadrantid observations, and the shower hasn’t been well covered for many years. Observers are therefore urged to make the best possible use of any clear skies during the shower’s activity period in 2006. |
