Active July 23-August 20
Radiant RA 03h 04m Dec +58°
The undoubted stand-out for meteor observers in the summer of 2007 is a very favourable return of the Perseids, peaking on Aug 13d 02h UT in dark, moonless skies. At this time, just as dawn is approaching for observers in the British Isles, the Perseid radiant will be high in the eastern sky and from locations away from artificial light pollution rates of around a meteor per minute should be attained. In most years, the Perseids produce corrected ZHR around 80 at maximum, with rates at half that level on Aug 11-12 and 13-14. Indeed, watches on any night in the 10-day interval centred on Perseid maximum are likely to be very productive for the patient observer: this is a great time for new observers to try their hand at meteor work!

All else being equal, best rates are found when the Perseid radiant – near the ‘Sword Handle’ on the Perseus-Cassiopeia border – is highest in the sky during the pre-dawn hours. Even in early evening, however, the radiant is already quite favourably placed:

Local Time (53oN)   Radiant Altitude     Local Time    Radiant Altitude
21h                             28.1°                                     01h                  52.8°
22h                             32.8°                                     02h                  59.3°
23h                             38.4°                                     03h                  67.1°
00h                             44.7°

Observers should bear in mind the nightly eastwards ‘drift’ of the Perseid radiant e to Earth’s orbital motion. In early August, the radiant is 15 degrees west of its position at maximum (given above), to the north of Andromeda.

New Moon falls on August 12, and the Perseid maximum night of Aug 12-13 (a Sunday to Monday) will be free from lunar interference. Productive watches become possible from about Aug 6-7 onwards, with the waning crescent Moon retreating into the morning sky and rising later from night to night.

Perseid meteors are produced by debris from Comet 109P/Swift-Tuttle. Incoming meteoroids have atmospheric entry velocities of 60 km/s, resulting in very fast meteors. A healthy proportion of Perseids are bright, making the shower a good target for photography. Perseids brighter than about magnitude 0 can be captured at film speeds of ISO 400 or greater with a camera fitted with either a 50 mm standard lens or 28 mm wideangle lens at f/2.8 or faster, using time exposures aimed towards Cygnus or the Square of Pegasus. These need not be driven – ‘static’ cameras yield images with meteors appearing as longer streaks cutting across the short arcs of star trails. Users of conventional film can try exposures of 10-15 minutes’ duration. Some observers enjoyed success with digital exposures of 30 seconds’ duration in 2005: obviously, these demand availability of sufficient memory as a night’s operation may amount to as many as 500 images!

Being fast meteors, Perseids – particularly the brighter examples – often leave behind persistent ionisation trains.

As one of the year’s most consistent very active showers (alongside the Quadrantids and Geminids), the Perseids justifiably enjoy favour with even casual observers. The 2005 return was well-observed from the UK, showing a typical strong peak with ZHR 70-80 and the usual abundance of bright events. It appears that the enhanced Perseid activity attending the 1992 perihelion return of the parent comet is now behind us, but the shower’s regular, fairly dependable performance makes this a continued highlight of the meteor observer’s year. Circumstances of the shower could hardly be more favourable for the UK in 2007, both in terms of the absence of moonlight, and the timing of maximum: observers should make the most of this opportunity – moonlight will severely restrict viewing in 2008.
   
Observations of these, and other less-active showers, together with sporadic activity, will be welcomed by the Meteor Section. Observing instructions can be found on the website at http://www.britastro.org/meteor
Send reports and enquiries to the Meteor Section Director:

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