Following early January’s Quadrantids, the opening months of the year are generally regarded as a rather thin time for meteor observing, with only minor shower and low background sporadic activity in evidence. Even the most dedicated observers find the minimal rates - sometimes only one or two meteors per hour - in February and early March rather a trial on their patience. 

Virginids

Active March and April

Radiant  RA 14h 04m Dec -09^o

                     13h 36m        -11^o

Activity begins to pick up a little from late March with the arrival of the Virginids. The shower is part of an essentially year-long ‘drizzle’ of meteor activity from close to the ecliptic plane. In common with other near-ecliptic showers, the Virginids show a split radiant, presumably a consequence of gravitational perturbations by the planets. Activity comes from radiants in the Virgo ‘Bowl’, and to the east of Spica, fairly low in the southern spring sky for UK-based observers. A result of the low radiant elevation is that Virginid meteors can, on occasion, have long, slow ‘grazing’ trajectories up from the horizon towards the zenith.

Observed Virginid rates are typically low, usually no better than 2-3 meteors/hr in late March and early April. The meteors can, however, sometimes be reasonably bright by way of reward for the patient observer. Watches in the post-midnight hours are likely to be most productive, and the dark of the Moon interval from about 28 March until mid-April will be the most favourable time to observe this low-activity, poorly-covered shower.

Lyrids

Active April 19-25

Radiant RA 18h 98m Dec +32^o

Usually, the shower which ‘re-opens’ the more active part of the meteor observer’s year, the Lyrids are unfortunately-timed in 2008. The Moon is only three days past Full at their April 21-22 maximum, and rises before the radiant has really climbed into the northeastern sky.

Eta Aquarids

Active April 24-May 20

Radiant RA 22h 20m Dec -01^o

An excellent shower for observers at southerly latitudes, the Eta Aquarids present a considerable challenge for those in the British Isles. The shower radiant, near the ‘Water Jar’ asterism in Aquarius, is only just beginning to climb in the eastern sky as dawn breaks in early May.

Radiant elevation at 53^oN

Local Time     Alt 

02                    3.9^o

03                  12.8^o

04                  21.0^o

Observations are hampered by the bright twilit skies. By the time nautical twilight has set in (Sun less than 12^o below the horizon), faint stars and meteors are hard to see; astronomical twilight (Sun 12-18^o below the horizon) allows brighter meteors to be seen. The observing window becomes more limited the farther north one goes:

Latitude       Onset of Twilight (May 4):  Astronomical      Nautical

57^oN                                                         All night              0208

55^oN                                                         0052                    0229

53^oN                                                         0131                    0245

51^oN                                                         0157                    0300

The Eta Aquarids are, like October’s Orionids, produced by debris shed from Comet 1P/Halley, and are extremely swift meteors, often leaving short-duration persistent trains. Peak activity occurs over several nights close to May 4, and observers seeking a challenge might wish to make use of the last hour or so of darkness on mornings around the Bank Holiday weekend to obtain watch time on this elusive shower: many very experienced northern-hemisphere meteor-watchers have never seen an Eta Aquarid! The Moon is New on May 5, and won’t interfere.

Alpha Scorpiids

Active April 20-May 19

Radiant RA 16h 31m Dec -24^o

                    16h 04m        -24^o

Ophiuchids

Active May 19-July

Radiant RA 17h 56m Dec -23^o

                    17h 20m        -20^o

Continuing the near-ecliptic trickle of low activity through early summer, these two showers offer only low rates for observers willing to persevere with the permanently twilit skies. As with the earlier Virginids, the meteors can sometimes be long, slow and reasonably bright as they climb from the low southern sky.

Capricornids

Active July-August

Radiant RA 20h 44m Dec -15^o

                    21h 00m        -15^o

July finally sees a significant upturn in overall meteor activity, including improved background sporadic rates. The Capricornids, active from early in the month, are a rather poorly-defined shower from the near-ecliptic region, with possible maxima on July 8, 15 and 26. The first two of these are favoured by an absence of moonlight in 2008, but observed rates are never likely to be higher than one or two per hour.

Alpha Cygnids

Active July-August

Radiant  RA 21h 00m Dec +48^o

Throughout July and August, a  steady trickle of one or two meteors/hr is reported from an apparently stationary radiant near Deneb, high in the UK summer sky. In theory, meteor shower radiants should move eastwards by roughly a degree per day, thanks to Earth’s orbital motion, and there are therefore some doubts as to whether the Alpha Cygnids are a genuine shower, or simply the result of observers aligning sporadic activity to a radiant close to a conveniently bright star.

Late July brings us into the most substantial active meteor period for the summer, with the combined output of the Delta Aquarids, Alpha Capricornids, Iota Aquarids, Piscis  Australids and Perseids making for productive watches as the skies begin to darken once again following the Summer Solstice. The Moon is at Last Quarter on July 25, and as it retreats further into the morning sky during early August, observers can look forward to some excellent watches, weather permitting.

Delta Aquarids

Active July 15-August 20

Radiant RA 22h 36m Dec -17^o

                     23h 04m       +02^o

The Delta Aquarids are the most productive of several showers with radiants south of the Square of Pegasus, still rather low in British skies on a July-August night. The shower has two branches, the southern being the more active: peak for this branch is on July 28-29, and shouldn’t be too badly affected by moonlight (the Moon is a waning crescent, rising around 00h local time) .

Radiant elevation at 53^oN

Local Time              D-Aq N      D-Aq S

22                             14.1^o           2.1^o

23                             22.4^o           9.1^o

00                             29.7^o         14.8^o

01                             38.5^o         18.5^o

02                             38.5^o         20.0^o

03                             38.7^o         19.1^o                 28-29 July

The Delta Aquarids’ northern branch, with its radiant near the ‘Water Jar’, is better-placed (higher in the sky) for UK observers, and peaks on August 6-7, with the Moon well out of the way (setting in early evening).

Radiant elevation at 53^oN

Local Time              D-Aq N      D-Aq S

22                             19.1^o           6.4^o

23                             26.9^o         12.7^o

00                             33.2^o         17.2^o

01                             37.5^o         19.7^o

02                             37.5^o         19.7^o

03                             33.3^o         17.5^o                 6-7 August

Peak Zenithal Hourly Rate (ZHR, allowing for sky transparency and radiant elevation) for the Northern Delta Aquarids is about 10, perhaps corresponding to observed rates of 5-6 per hour under good conditions. Most Delta Aquarids are medium-velocity meteors in the magnitude +2 to +4 range; the shower is not particularly noted for an abundance of bright events.

Alpha Capricornids

Active July 15-August 20

Radiant  RA 20h 36m Dec -10^o

Although comparatively weak (ZHR 5), the Alpha Capricornids are a distinctive shower, producing long, slow meteors which can sometimes be notably bright. Observers conducting watches in early August can expect to record one or two ‘Alpha Caps’ per hour, and the nominal peak on August 2-3 is well-placed with respect to moonlight - the Moon is New on August 1 and therefore won’t interfere. The radiant is close to the wide naked-eye pair of Alpha and Beta Capricorni, fairly low in the southern sky on an August night.

Iota Aquarids

Active July-August

Radiant RA 22h 10m Dec -15^o

                    22h 04m        -06^o

Like the Delta Aquarids, a shower with a double radiant. At peak, on August 6-7, the Iota Aquarid radiants lie roughly 10 degrees east of those of the Delta Aquarids, and care must be taken to distinguish the two showers. Iota Aquarid meteors are mostly faint and quite swift

Piscis Australids

Active July 15-August 20

Radiant RA 22h 40m Dec -30^o

Further complicating the radiant profusion in the low summer sky, the Piscis Australids are a rather minor stream, producing slow, long meteors. The radiant’s low altitude from UK locations means that rather few of these are reported by BAA observers.

Perseids

Active July 23-August 20

Radiant RA 03h 04m Dec +58^o

Always the summer’s main attraction for meteor observers, the Perseids are expected to peak around August 12d 09h UT, making the Monday night to Tuesday morning of Aug 11-12 probably the shower’s most productive in 2008. Good observed rates can be expected particularly in the early hours after the waxing gibbous Moon has set (around 23h 20m local time on Aug 11-12). Observers watching late on Aug 11-12 should experience increasing activity towards dawn: from a clear, dark location rates of a meteor per minute might be seen in the latter parts of the night as the shower radiant (near the Double Cluster on the Perseus/Cassiopeia border) climbs high into the eastern sky. Activity should be starting to decline by the time darkness falls on Aug 12-13.  Moonlight becomes a nuisance after maximum, but even as late as Aug 13-14 it should still be possible to follow the Perseids’ immediate decline from peak, with at least a couple of hours of dark sky between moonset and dawn.

Perseid Radiant at 53^oN

Local Time       Altitude

21h                      28.1^o

22h                      32.8^o

23h                      38.4^o

00h                      44.7^o

01h                      52.8^o

02h                      59.3^o

03h                      67.1^o

Perseid activity is evident as early as the third week of July. The main part of the shower, including its steady rise through the first 9 days or so of August, will enjoy dark skies. Activity takes a marked ‘kick’ around August 8-9, and watches between this date and August 14-15, particularly, should be very rewarding.

The Perseids are associated with Comet 109P/Swift-Tuttle, which was last at perihelion in 1992. Enhanced activity accompanied that return, and was evident for several years, up to at least 1997. The 2005 and 2007 Perseids - our most recent well-covered returns of the shower - proved fairly ‘normal’, with a single sharp peak to ZHR ca. 80 in 2005 (perhaps slightly lower - ca. 70 - in 2007), and the usual slow rise to and steep decline from maximum. As always the 2008 return of the shower requires careful scrutiny on all possible clear nights (and not just at maximum!).

The Perseids are well known for the abundance of fast, bright meteors close to their maximum. Perseid meteoroids enter the atmosphere at a velocity of 60 km/sec, and the resulting meteors often leave behind persistent ionisation trains.

The large numbers of bright events in the five-day interval centred on Perseid maximum makes this an excellent target for photography. Conventional film remains the medium of choice for most observers. Exposures, which can be with a static (undriven) camera, of 10-15 minutes’ duration, using ISO 400 film and a 50 mm or wideangle 28 mm lens at f/2.8 or faster, can capture meteors of magnitude 0 and brighter. Ideal aiming directions are about 20-30 degrees to one side of the radiant at 50 degrees altitude above the horizon - Cygnus in early evening, the Square of Pegasus later in the night, or towards the north celestial pole, for example

Observations of any of the above showers, made by the BAA Meteor 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

(01243) 782679

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