British Astronomical Association
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British Astronomical Association
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Meteor Section |
Unfavourable lunar phasing circumstances have been the dominant theme through most of 2003, with bright moonlight compromising observations of the most active meteor showers close to their activity maxima. Through the winter months, this situation continues, limiting viewing opportunities for the Geminids and Quadrantids, but things are set to improve in 2004! As outlined below, there is still plenty of scope for at least some useful meteor work.
Geminids
Active December 7-16
Radiant RA 07h32m Dec +33o
BAA observers have obtained many useful data on this shower over the past 25 years, charting an increase in intensity and broadening of the maximum, which occurs around December 13-14. Having had a fairly narrow peak in the 1960s, the Geminids currently how activity in excess of that found during a typical Perseid maximum over a 36-hour interval it is usually the case that watches on Dec 12-13 and/or 14-15 can be almost as productive, in terms of meteor numbers, as those on maximum night. Corrected peak Geminid Zenithal Hourly Rate in recent years has been of the order of 100-12-0, corresponding to observed rates up to 80 meteors/hr and more. Commonly, the meteors come in 'clumps', and it is not uncommon for spurts of four or five Geminids to be reported in a minute, following which there may be a brief lull in activity.
The Geminid radiant lies just north of Castor, and is above the horizon throughout the hours of darkness in the British Isles in mid-December, reaching its highest elevation around 01h local time; productive watches are possible from mid-evening onwards.
Geminid meteors are produced by debris from asteroid (3200) Phaethon. The meteoroids have a rather different - rocky, as opposed to dusty - nature from those in cometary streams such as the Perseids or Leonids, meaning that they are mechanically more robust and last longer in luminous flight, penetrating the atmosphere to somewhat lower altitudes. Their relatively slow entry velocity (35 km/s) and reasonably abundance of bright events make the Geminids a good photographic target.
The 2003 return is rather affected by moonlight. Full Moon falls on December 8, essentially wiping out the early parts of the shower. Maximum activity is expected to centre around Dec 14d 10h UT (during morning, daylight hours in the UK). For observers in the British Isles, best visual rates can probably be expected in early evening before the gibbous Moon rises on the Sunday-Monday of December 14-15. Moonrise occurs around 21h local time on this night, at which time the radiant will have attained an elevation of just over 30 degrees in UK skies.
A well-documented feature of the shower is the increased proportion of bright Geminids in the interval after the very highest visual rates. It is possible that although numbers will be gradually declining as time goes by on Dec 14-15, observers will find the activity laved with occasional very bright and spectacular Geminids.
The pre-maximum night of Dec 13-14 offers a shorter dark sky 'window' (moonrise ca 20h local time), while the rates on Dec 15-16 (moonrise ca 22h 30m) will be well down. Nonetheless, observers are encouraged to make use of any available clear skies on these nights, too!
Prospects for the Geminids in 2004 are very much better, with a New Moon at maximum, and encounter circumstances very similar to those which brought about the memorable return of 1996 which was marked by very high rates and numerous fireballs.
Ursids
Active December 17-25
Radiant RA 14h 28m Dec +78o
Occurring just before Christmas, this shower (produced by debris from Comet 8P/Tuttle) is always somewhat neglected. In a lot of ways, this is a pity - activity at a 'normal' return can be the equal of the much better-covered Lyrids of April, and the shower is prone to occasional outbursts of enhanced activity. The 2003 return, with peak on Mon-Tues Dec 22-23, is well-placed with regard to moonlight; New Moon is on Dec 23, offering dark skies.
The Ursid radiant, near the 'Guardians of the Pole' in Ursa Minor, is circumpolar from the British Isles. Its minimum elevation is reached as it makes lower culmination due north in mid-evening. By the early morning hours, the radiant is climbing in the northeast.
Typical observed rates may be only of the order of 6-7 meteors/hr. Ursids are fairly swift, but the shower is not especially noted for producing bright events. The most recent outburst well seen from the UK was in 1982, when observed rates reached 20 meteors/hr. A yet stronger return was seen by observers in mainland Europe in 1986, but a 1994 outburst reported in IMO literature was not confirmed by contemporaneous observations by BAAMS members. Quite how common interludes of enhanced Ursid rate may be is uncertain: more observations are needed!
With long hours of darkness and the radiant above the horizon night-long, perhaps an hour or two of watch time on this neglected shower provides a productive alternative to the annual Festive televisual nadir?
Quadrantids
Active January 1-6
Radiant RA 15h 28m Dec +50o
Opening the New Year is one of the three most active regular showers. The Quadrantids have, at past returns, been found to produce peak ZHR 120-140, as in 1992. The maximum is, however, rather narrow, with most of the high activity occurring in a 6-hour interval; Watches outwith this period typically yield only low Quadrantid rates.
Maximum in 2004 is expected to centre around Jan 4d 04h UT, a couple of hours before dawn on the Saturday night to Sunday morning of January 3-4. Unfortunately, moonlight is a very major player. The Moon, a couple of days before Full, will be up for most of the night, setting about 90 minutes before dawn begins to lighten the sky. Lunar glare will restrict useful observations to the last couple of hours of the night. With, potentially, high rates at this time, it may still be worth rising early to catch the Quadrantids.
The Quadrantid radiant lies in northern Bootes, east from the 'handle' of the Plough, and is at its highest at the end of the night (about 50 degrees up in the northeast from UK latitudes). Quadrantid meteors are medium-paced, and the brighter examples sometimes show a pronounced blue or green colouration.
Following the Quadrantids, meteor rates reach their minimum for the year: even dedicated regular observers find the interval from mid-January to mid-March disappointing, with only a thin trickle of sporadic and minor shower activity in evidence. The situation improves slightly in March as the Virginids - from radiants in the Virgo 'bowl' and just east of Spica - become active. The next really pronounced regular shower activity will come in the spring with a very favourable return of the Lyrids in April.
Observations will, as always, be welcomed by the Meteor Section. Standard observing instructions can be found on the VISUAL OBSERVING NOTES page at this site.
Page last updated: 29/03/2004