Every three years or so – roughly one-sixth of a Saros cycle – lunar phasing is such that the maximum of the Perseids is adversely affected by strong moonlight. This is, sadly, the case in 2006: Full Moon falls on August 09d, meaning that the shower’s peak on Aug 12-13 will be swamped by glare, and only the brightest meteors will be seen. This won’t deter ‘casual’ watchers – many local astronomical societies are doubtless planning barbeques/etc for the Saturday night – but productive serious, systematic watches are out of the question. Circumstances will be a whole lot better in 2007, when maximum is favourably-timed for western European longitudes in a moonless sky! For the meantime, observers have to make the most of the reasonable opportunities presented by the less prolific Capricornid and Aquarid showers active during late July’s Dark of the Moon. Coverage of these is just as important to the Meteor Section’s long-term work, and the combined activity from these radiants, coupled with reasonable sporadic rates, can make for productive viewing in the post-midnight hours.

Alpha Capricornids

Active July 15 – August 20

Radiant RA 20h 36m Dec –10°

Perhaps first shower to become noticeable from mid-July is the Alpha Capricornids, with a radiant on the western side of the dim ‘wedge’ of stars marking out Capricornus, southwest of the Square of Pegasus and low in the UK summer sky. Observed rates are never particularly high – even around the nominal peak on August 2, at best only maybe a couple of meteors per hour – but the shower is notable for producing long, slow meteors, some of which can be spectacularly bright. The ‘Alpha caps’ are believed to be associated with Comet 45P/Honda-Mrkos-Pajdusakova, and meteoroids from the stream have a slow atmospheric entry velocity of 23 km/s.
 

Delta Aquarids

Active July 15 – August 20

Radiant  RA 22h 36m Dec –17°

                     23   04        +02°

Most active among the late-July showers, the Delta Aquarids have a double radiant with Northern and Southern ‘branches’ south of the Square of Pegasus. The Southern, close to the star Delta Aquarii at the time of maximum on July 28-29, is the more active, but is rather low in UK skies even at culmination, late in the night around 02h UT. The Northern Delta Aquarid radiant is more favourably-placed, close to the inverted ‘Y’ of the Water Jar asterism: its peak, on Aug 6-7, will be severely affected by strong moonlight this year.

Delta Aquarids are medium-paced meteors (entry velocity 42 km/s). Very bright meteors are scarce in the shower; the bulk of the crop lie in the range from magnitude +1 to +4. Activity is at its best in the last week of July and first week of August, when observers might log as many as 6-8 meteors/hr from the shower. 

Piscis Australids

Active July 15 -  August 20

Radiant RA 22h 40m Dec –30°

With a radiant close to Fomalhaut, this shower is rather unfavourably placed for UK-based observers, but careful watchers may catch the occasional Piscis Australid during late July. The meteors are slow and sometimes bright: like Alpha Capricornids, they can – by virtue of the low radiant position – sometimes traverse long arcs upwards from the southern sky. 

Iota Aquarids

Active July – August

Radiant RA 22h 10m Dec –15°

                    22   04         -06°

Active at rather modest levels hroughout July and August, the Iota Aquarids have a double radiant, with Northern and Southern branches. These lie to the west (right, in UK skies) of those for the more prolific Delta Aquarids. Peak rates are found around August 6, so the best part of this shower will be somewhat taken by moonlight in 2006. A few shower members should be in evidence by late July. Most Iota Aquarids are faint.

Alpha Cygnids

Active July – August

Radiant RA 21h 00m  Dec +48°

Throughout the summer, observers record a steady trickle – one or two per hour – of meteors from a radiant close to Deneb, high in British skies at this time of year. It is a matter of debate whether this is a genuine shower with a radiant radiant that remains stationary throughout its activity period: most shower radiants drift eastwards by about a degree in Right Ascension per day as a result of Earth’s orbital motion.

Perseids

Active July 23 – August 20

Radiant RA 03h 04m Dec +58°

Although the most active period in the shower, close to Aug 12-13, will be largely wiped out by strong moonlight, observers can still catch a few meteors from this most popular of showers during late July and into the first few days of August, before the Moon becomes too intrusive. Even in late July, Perseid meteors can be bright and,m with their high entry velocity (59 km/s) leave reasonably long-lived persistent ionisation trains. Bear in mind that, in late July, the radiant will be some 10 degrees west of its maximum position (near the ‘Sword Handle’ in Perseus), so watch for Perseids at this time emanating from a point north of Andromeda. 
 

Kappa Cygnids

Active August 15-22

Radiant RA 21h 24m Dec +59°

The return of dark sky conditions as the Moon retreats after Perseid maximum favours the rather weak Kappa Cygnid shower. Peak rates, expected on Aug 17-18, are usually less than 5 meteors/hr. In past years, some spectacularly-bright yellow-blue Kappa Cygnid  fireballs have been reported. The meteors are slow, with an entry velocity of 25 km/s.
 

Alpha Aurigids

Active August 25 – September 6

Radiant RA 05h 36m Dec +42°

Moonless conditions in the closing week of August will favour observations of the minor Alpha Aurigid shower. The radiant, close to Capella, is well up in the northeastern sky by the early hours, and activity is fairly respectable, reaching a sky-transparency and radiant altitude-corrected peak ZHR around 10 close to the September 1-2 peak in most years. Outbursts of higher activity have been reported, most recently in 1986. Alpha Aurigids are swift, Perseid-like meteors (atmospheric entry velocity 66 km/s), with a reasonable proportion of bright events leaving persistent ionisation trains. 
 


Following the summer’s high activity period, the autumn months from September onwards will bring some good meteor observing opportunities. The Orionids are well-placed in the third week of October, while the Leonids offer the prospect of one last (relatively minor) outburst in moonless skies a couple of hours before dawn on November 18-19. Mid-December will afford at least a few decent hours of pre-moonrise dark sky viewing for the Geminids at their best. 

Observations, made by the Meteor Section’s standard methods – outlined elsewhere on these pages – will, as always, be welcomed by the Director.