The Geminids and Quadrantids: the season's grand finale

by Neil Bone

Lunar phasing in the second half of 1999 has certainly been advantageous for meteor observing, with most of the major shower maxima occurring during the dark of the Moon. The favourable conditions also extend to the Geminids this December, and the Quadrantids in early January. In recent years, meteor observers have come to look on the Geminids as the year's most reliably active shower. The 1996 return provided a most memorable night of maximum activity on Dec 13-14, with observed rates of 40-50 Geminids per hour for much of the time, and a plethora of bright events. The 1998 return was quite favourable, but poor weather intervened. Although BAA observers had reasonable skies late on Dec 12-13, before maximum, peak night was lost with most of Europe under cloud. Across the Atlantic, north American observers had better luck, and reports suggest activity comparable to that of 1996, including numerous bright events.

The Geminids are active between December 7-15 and show a steady build-up of activity to their broad (currently about 24-hour) maximum, which is followed by a steep decline. The rising phase in 1999 is certainly blessed by an absence of lunar interference, with New Moon on Dec 7. Maximum is expected around 10h UT on Dec 14, meaning that the highest rates should be seen in the post-midnight hours of Dec 13-14, and in the evening of Dec 14-15. By maximum, the Moon is nearing first quarter, and will interfere to some extent in the early evening, before setting around 22h UT on Dec 14.

The Geminid radiant lies just north of Castor, and is above the horizon all night during the shower's activity period, reaching its highest around 01h UT. Geminid meteors are slow-moving and can sometimes be spectacularly bright, making the shower an ideal target for photographers. Analysis by former Meteor Section Director George Spalding showed a clear change over time in the magnitude distribution in the Geminids close to maximum, with the bright events tending to come later. In all probability, Dec 14-15 will be more productive of bright Geminids.

The New Year opens with a more difficult shower to observe in the Quadrantids. The shower has a circumpolar radiant just north of Böotes. During the early evening hours, the radiant is fairly low over the northern horizon, and viewing circumstances are less than ideal. After midnight, and particularly towards dawn, however, it climbs much higher. Activity is present between January 1-6, but substantial rates are only seen within about 6-8 hours of the sharp maximum, expected to occur close to 2000 Jan 4d 04h UT - ideally-timed for observers in western Europe.

It has been some years since the British Isles enjoyed clear, moonless skies for the short-lived Quadrantid peak. The 1992 return produced excellent activity, with a sky- and radiant altitude-corrected peak Zenithal Hourly Rate around 120 in the early morning of Jan 4. Since then, we have either had clouds, moonlight, or a limited view of comparatively low activity on the flanks of the peak: most recently, in 1998 UK observers saw the Quadrantids falling away rapidly from an afternoon peak as the evening of Jan 3-4 wore on.

In contrast with the 1999 return, the 2000 Quadrantids are met by dark skies. The Moon will be New on Jan 6, and the waning crescent rising very late on Jan 4 is unlikely to trouble observers. Quadrantid meteors are medium-paced, and sometimes strongly coloured (blue and yellow meteors are commonly reported). Like the Geminids, they show some degree of particle sorting, with bright meteors (produced by large meteoroids in the stream, whose parentage remains uncertain) being most abundant after maximum. Photographic work in the later hours of the night on Jan 3-4 could be quite rewarding.

The Quadrantids bring the curtain down on the most active part of the year - stretching back to August's Perseids - for meteors. This has been a particularly busy spell in 1999-2000, with much attention focusing on November's Leonids. Between mid-January and April, only minor shower and low background sporadic activity is present, and there is little to attract the interest of any but the most dedicated meteor observers.

Observations of both the Geminids and Quadrantids will, of course, be welcomed by the Meteor Section. Guidelines on visual work can be obtained on the Section's Web pages at http://www.ast.cam.ac.uk/~baa/meteor1.html or from the Director at the address on the inside cover of the Journal. Clear skies in mid-December for a healthy Geminid peak may lead meteor observers to conclude that Christmas has come early, while many will certainly be making it their New Year resolution to get some watch time in for the Quadrantids on the Monday night/Tuesday morning of January 3-4, before the onset of the long quiet season.

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