Autumn in the northern hemisphere is the prime observing season for meteor enthusiasts. Following the Perseids in August, several further showers come to prominence during October-December. ‘Peak season’ is rounded off by the Quadrantids in early January, following which activity reaches something of a trough.

Even at times when major shower activity is not expected, the ever-present background sporadic meteor population can provide sufficient rates - perhaps 10-12/hr in the early hours on a September morning - to reward patient watchers.

Piscids

Active Throughout September-October

Radiants RA 00h36m Dec +07^o

               RA 00h24m Dec   00^o

               RA 01h44m Dec +14^o

For much of the year, a ‘drizzle’ of meteor activity is detectable emanating from the vicinity of the ecliptic plane. Observed rates are typically low - perhaps only a couple of meteors per hour - and the meteors are generally slow and of moderate brightness. The Piscids are part of this activity, showing possible peaks in activity around 8 and 21 September, and 13 October.  

Orionids

Active 16-31 October

Radiant RA 06h24m Dec +15^o

One of two annual showers associated with Comet 1P/Halley (the other being the Eta Aquarids of early May), the Orionids are a moderately active shower, usually producing observed rates in excess of 10 meteors/hr around their maximum. Thanks to the 'filamentary' nature of the debris stream laid down by the parent comet, activity can vary markedly from one year to another: good rates can be experienced if Earth encounters a rich meteoroid filament, but at other times activity might seem disappointing. Several sub-peaks are usually seen between 20-22 October, and intervals of slightly increased activity can be found even as late as 27-28 October. Like 1P/Halley, stream meteoroids have a retrograde orbit around the Sun, meaning that they enter the upper atmosphere on 'head on' collisions at the high velocity of 66 km/sec. Orionid meteors are very swift, and the brighter ones, particularly, often leave behind brief persistent ionisation trains.

Having been laid down over numerous returns of 1P/Halley, the Orionid meteor stream is quite spread out, and this is reflected in the shower's diffuse (probably multiple) radiant. Orionids emanate from a region of sky midway between Betelgeuse (Orion’s eastern ‘shoulder’) and the second-magnitude star Gamma Geminorum. The radiant doesn’t rise until 22h local time, and best rates are generally found in the early morning hours once it has gained somewhat in altitude.

Local Time      Radiant Altitude (53^oN)   Local Time    Radiant Altitude (53^oN)

       22h                       8.5^o                            03h                     48.7^o

       23h                     17.6^o                            04h                     51.7^o        

       00h                     26.5^o                                      05h                     51.3^o

       01h                     35.1^o                            06h                     47.4^o

       02h                     42.8^o

In 2006, observers in North America, particularly, reported higher-than-normal Orionid rates. Poor weather unfortunately restricted observations from the British Isles. While there is no reason to expect unusual activity in 2007, the shower is still an important target for observation.  Only the earlier parts of the shower, up to  and including the 20-22 October maximum period, are really favoured for observation this year. The Moon reaches First Quarter on 19 October, at that time setting before midnight local time just as the Orionid radiant is starting to climb, and leaving dark skies for the early hours. By 24 October, however, the bright waxing gibbous Moon is an intrusive presence until 04h local time.

Taurids

Active 20 October - 30 November

Radiants N RA 03h44m Dec +22^o

               S RA 03h44m Dec +14^o

Observers carrying out watches for the Orionids may catch some slow meteors from the Taurid shower, produced by debris from Comet 2P/Encke. The shower is active for several weeks (a consequence of the ancient debris stream’s spread due to gravitational perturbations by the major planets) and the rates-profile is rather ‘flat’ compared with those of shorter-duration showers like the Perseids or Orionids. A broad peak is seen over about ten days, centred around 3 November, when observed rates of 5-7 meteors/hr may be found.

Taurids come from two radiants - a northern branch which lies close to the Pleiades in early November, and a southern which is then a few degrees west of the Hyades. Note that the co-ordinates given above relate to the radiants' positions at  maximum: thanks to Earth’s orbital motion around the Sun, the radiants appear to move eastwards by about a degree per day, and this should be taken into account of observing in, say, mid-November.

The Taurids are sometimes described in the popular literature as a shower rich in fireballs (meteors of  magnitude -5 or brighter). In practice, while  moderately-bright Taurids in the range from mag. 0 to -3 are quite often seen, in most years the shower is not necessarily replete with really spectacular meteors. There are exceptional years - 2005 being the most recent - when Earth encounters enriched trails or ‘swarms’ of larger material in the Taurid stream, and under such circumstances fireballs are more numerous.

What can make Taurids appear particularly impressive is their slow atmospheric entry velocity (27-29 km/sec) and long duration  in luminous flight. The shower’s most active period is compromised somewhat for UK residents by its coincidence with ‘firework season’. In 2007, at least absence of moonlight will be of some advantage: the Moon is New on 9 November, offering darker late-evening skies during the opening fortnight of the month. Like many others, this is a shower which merits more attention than it has received from observers in recent years.

Leonids

Active 15-20 November

Radiant RA 10h08m Dec +22^o

By contrast, November’s other major shower has been the focus of a great deal of attention over the past decade or so. The 1998 return of parent comet 55P/Tempel-Tuttle brought the expected enhancement in Leonid activity, with meteor storms (by loose definition, intervals during which the ZHR reached 1000 or more) in 1999, 2001 and 2002. A marked increase in activity over normal levels occurred much as forecast on 19 November 2006. Now, however, with the comet long-since departed from  the inner Solar System, Leonid activity can be expected to settle into the more ‘regular’ pattern seen for roughly two-thirds of the shower's 33-year cycle.

That doesn’t mean that the shower is a poor target for observation! In the mid-1980s, for example, observers who carried out watches on the shower were rewarded with rates of up to 10-12 meteors/hr, and even during the quieter years Leonid activity is laced with a reasonable proportion of bright events. Another stream in a retrograde orbit, the Leonids impact on the upper atmosphere at 70 km/sec, and these high-energy collisions produce not only bright events, but also persistent ionisation trains which can sometimes be of exceptionally long duration (up to several minutes).

The annual shower peak is expected around 05h UT on 17-18 November - just before daybreak over the British Isles on a Saturday night to Sunday morning. As with the Orionids, this is a shower best observed in the post-midnight hours: the radiant, in Leo’s ‘Sickle’ asterism, rises around 23h local time, and is highest in the sky a  dawn approaches.

Local Time     Radiant Altitude (53^oN)      Local Time     Radiant Altitude (53^oN)

      23h                       6.4^o                                03h                     41.4^o

      00h                     14.7^o                                           04h                     49.4^o

      01h                     23.6^o                                05h                     55.6^o

      02h                     32.6^o                                06h                     58.8^o

While very high activity is now unlikely until the 2020s, observations of the ‘quiet time’ Leonids provide a very useful baseline for comparison with past and future returns.

Geminids

Active 7-16 December

Radiant RA 07h32m Dec +33^o

Currently the most active of the regular annual showers, with rates outstripping those of even the Perseids for a 24-hour interval centred on  their 13-14 December maximum, the Geminids are a real treat for observers prepared to brave the winter cold! Unusual in being associated with an asteroid - (3200) Phaethon - rather than a comet, the shower has grown in intensity since the 1980s as a result of the meteor stream orbit being dragged gradually outwards across that of the Earth. A consequence is that we currently encounter the most densely-populated parts of the meteor stream. This happy situation is temporary unfortunately - in a few more decades, Geminid displays can be expected to diminish in intensity. Here we have an excellent opportunity to follow, year on year, the evolution of a meteor stream.

Geminid meteors enter the atmosphere at a relatively slow 35 km/sec, and thanks to their robust (presumably rocky/asteroidal as opposed to dusty/cometary) nature tend to last longer than most in luminous flight. Unlike swift Perseid or Orionid meteors, which last only a couple of tenths of a second, Geminids may be visible for a second or longer, sometimes appearing to fragment into a train of ‘blobs’. Their low speed and abundance of bright events makes the Geminids a prime photographic target.

Activity is expected to peak around Dec 14d 11h UT - during UK daylight. The maximum is broad, however, and observations on the Thursday night to Friday morning of Dec 13-14 should be productive even ahead of peak, especially late on in the night when the radiant  (just north of Castor) is high in the sky - see table below. The evening of Dec 14-15 is also likely to be graced with high Geminid activity, with the added bonus of an increased proportional abundance of bright events. Past observations show that bright Geminids become more numerous some hours after the rates have peaked, a result of particle-sorting in the meteor stream. The interval during which the brightest Geminids typically occur coincides with the early evening hours of Dec 14-15 at UK longitudes: under similar circumstances in 2003, several spectacular Geminids were seen.

Local Time    Radiant Altitude (53^oN)     Local Time    Radiant Altitude (53^oN)

20h                                    25.4^o                     00h                          60.5^o

21h                                    34.1^o                     01h                          67.1^o

22h                                    43.1^o                     02h                          70.0^o

23h                                    52.1^o                     03h                          67.4^o

In recent years, the Geminids have shown typical peak observed rates of 50-60 meteors/hr in good skies. Wrap warmly and enjoy the show!

Quadrantids

Active 1-6 January

Radiant RA 15h28m Dec +50^o

The New Year opens with very favourable conditions for the Quadrantids, one of the three most active regular annual showers. Poorly observed in most recent years thanks to a combination of factors – a very narrow period of high activity, poor January weather, and moonlight interference in at least one year out of three! – the shower was last well-covered by BAA observers in 1992, when peak ZHR 120-140 was found. Activity is close to peak levels for only about six hours: at other times, only a ‘trickle’ of a few meteor per hour might be detected.

Timing of the Quadrantid peak on 2008 is very favourable from the UK perspective: the shower maximum is expected around Jan 04d 05h UT, just before dawn at our longitudes. Observations in the hours after midnight on the Thursday night to Friday morning of Jan 3-4 will be most productive. At this time, the Moon will be a waning crescent a  few days from New, offering dark skies.  

The Quadrantid radiant lies in northern Bootes, and from the latitudes of the British Isles is actually circumpolar. As the table below shows, the radiant is low in the northern sky during the evening hours, but climbs to a very favourable elevation as dawn approaches - in 2008, the Quadrantid peak comes with the radiant high in the eastern sky.

Local Time     Altitude (53oN)            Local Time     Altitude (53oN)

17                    22.5^o                             00                    21.8^o

18                    18.1^o                             01                    27.2^o

19                    14.9^o                             02                    33.3^o

20                    13.3^o                             03                    41.8^o

21                    13.1^o                             04                    49.0^o

22                    14.6^o                             05                    56.9^o

23                    17.5^o                             06                    66.3^o

Quadrantids are, like the Geminids, relatively slow meteors, with atmospheric entry velocity 42 km/sec, 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 (another similarity with the Geminids!), a possible break-up product of Comet 1490Y1 following the latter’s close approach to Jupiter in 1650.

Much of the high activity close to the peak is comprised of moderately bright to faint meteors: as a result of particle-sorting brighter Quadrantids (produced by larger meteoroids) become more numerous following the maximum, and might be in evidence by the very end of the night on 2008 Jan 3-4.

The Quadrantids can certainly be listed as a shower very much in need of observation – so why not make it your New Year’s Resolution to start 2008 with a few hours of meteor watching in the early hours of Jan 3-4!

Observations of any of the above showers, made by the Section’s standard methods outlined elsewhere on these pages will be welcomed by the Director:

Neil Bone

‘The Harepath’, Mile End Lane, Apuldram, Chichester, West Sussex, PO20 7DZ