In partnership with the BAA Project Perseid 2010, the Beyond International Year of Astronomy project is running Meteorwatch to encourage members of the public who may never have even seen a meteor to go out and look for one and then use twitter to tell others about their experience.
Always the summer’s main attraction for meteor observers, this August’s display of the Perseid meteors should be particularly favourable given that the peak occurs just a couple of days after New Moon and, consequently, there will be absolutely no interference from moonlight. It is hoped that observers will make every effort to cover the shower well this year, and send in their observations to the BAA Meteor Section.
When to Observe
Perseid activity may be evident as early as the third week of July, although there will be considerable interference from moonlight at the end of July since the Moon is Full on July 26. Activity takes a marked ‘kick’ around August 7/8, but by this time the Moon will be virtually New and watches may be carried out from this date right through until August 15/16 under dark, moonless skies. It is hoped that, weather permitting, observers will cover shower activity throughout this period, including nights away from the main peak.
The Perseids are expected to peak around 22h UT on August 12, making the hours from dusk on August 12 to dawn on August 13 probably the most productive for observers in the UK this year. Good observed rates may be expected in the early morning hours on August 11/12 and 12/13 as the shower radiant (RA 03h 04m Dec +58o) climbs high into the eastern sky. Perseid shower activity will be starting to decline by the time darkness falls on August 13.
All else being equal, the best observed rates are found when the Perseid radiant – near the ‘Sword Handle’ star cluster on the Perseus-Cassiopeia border at maximum– is highest in the sky during the pre-dawn hours. However, even in the early evening, the radiant is already at quite a favourable altitude as the table below shows:
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 due 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.
The Parent Comet
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 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. In 2008, there was a notable sharp spike in activity rising to in excess of 100 m/h after the ‘normal’ maximum. As always, the 2010 return of the shower requires careful scrutiny on all possible clear nights (and not just at maximum!). The normal limits of the shower are from July 23 until August 20.
Photography
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, considering the absence of interference from moonlight this year. Conventional film now remains the medium of choice for relatively few observers, with most having made the transition to digital SLR cameras.
With a static (undriven) digital camera, mounted on a sturdy tripod, and operated by a pre-programmed digital timer control unit, exposures should be kept short – about 30 seconds duration – with the speed set to ISO 1600 and a wide-angle lens set to maximum aperture. Remember that a super wide-angle 20mm focal length lens on a Canon DSLR, for example, has the coverage of only a 32mm lens on a full frame 35mm camera and 18mm becomes the equivalent of a 29mm lens on 35mm full frame. Such a set up, under good sky conditions, 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 the early evening, the Square of Pegasus later in the night, or towards the north celestial pole, for best results.
Reporting of Observations
For further information, or copies of report forms, observing notes, and details of how to carry out group meteor watches, please visit the BAA Meteor Section website at http://britastro.org/meteor or contact the Acting Director of the BAA Meteor Section.
A new simplified explanation of how to fill in the visual meteor report form is coming here soon.
An electronic version of the visual meteor report form may be found here:
 Meteor_Section_Visual_Report_Blank.xls
Please submit your observations to the BAA Meteor Section as soon as possible after you have made them, and at any rate within one month at the most. Observations should be sent to the Acting Director, who will be pleased to answer any queries regarding further aspects of meteor work.:-
Dr John Mason, 51 Orchard Way, Barnham, West Sussex PO22 0HX.
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