[BAA-ebulletin 00688] PERSEID METEOR SHOWER 2012

[Rick]

[BAA-ebulletin 00688]  PERSEID METEOR SHOWER 2012
(c) 2012 British Astronomical Association    http://www.britastro.org/

PERSEID METEOR SHOWER 2012

Always the summer's main attraction for meteor observers, this August's display of the Perseid meteors should be quite favourable given that the peak occurs just a few days before new Moon. Consequently, there will be only slight interference from the waning crescent Moon (on the Taurus/Gemini border) just before dawn.

It is hoped that observers will make every effort to cover the peak of the shower well this year. Meteor observing is a particularly good activity for local societies and the BAA Meteor Section welcomes reports from such groups.

Experienced observers have already reported early activity from the Perseid shower.  Peter Meadows and Nick James managed to capture a nice bright Perseid (displaying in-flight and terminal bursts) with their video imaging systems on Saturday, 4th August at 23:56 UT.

WHEN TO OBSERVE

Perseid rates normally take a marked 'kick' upwards around August 8, and with the Moon now on the wane, watches may be carried out in darkening skies from now right through until the end of the shower's normal period of activity on August 20, a few days after New Moon. It is hoped that, weather permitting, observers will cover shower activity throughout this period, even on nights away from the maximum.

The Perseids are expected to peak around 10h UT on Sunday, August 12, making the late evening and pre-dawn hours of August 11/12 and the following night of August 12/13 probably the most productive for observers in the UK this year. Good observed rates may also be expected in the early morning hours on August 10/11 and 13/14 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 14.
 
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 - is highest in the sky during the pre-dawn hours. However, even in the early evening (when there will be absolutely no interference from moonlight), the radiant is already at quite a favourable elevation above the horizon.

With cloudless skies, and in a dark viewing site, observers can expect to see between 50 and 70 meteors each hour near the peak. Even in light polluted towns or cities observed rates may still be around ten an hour in the early morning hours when the radiant is high.

VISUAL OBSERVATIONS

The BAA's visual meteor report forms, available as downloads in both pdf and Excel formats, enable observers to record the time of occurrence, apparent magnitude, shower membership (or if sporadic), constellation in which seen, and details of any persistent train or other characteristics, for each meteor seen. Watches should ideally be of an hour's duration or longer (in multiples of 30 minutes).  Observers should also carefully record the observing conditions and the stellar limiting magnitude.

Visual observers are invited to submit their observations electronically, using the new BAA report forms, to meteor at britastro dot org. (See the Meteor Section's Observing Notes.)

IMAGING

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 digital imaging, considering the low level of interference from moonlight this year. Conventional film is now the medium of choice for very few observers, with most having made the transition to digital SLR cameras.

With a tripod-mounted camera, lens (usually a wide-angle) at full aperture and a high ISO setting, the observer hopes that a bright meteor will flash through the field of view while the shutter is open. Digital SLRs (DSLRs) are very efficient at collecting background light from the sky, particularly at a setting of ISO 1600, so exposures should generally be kept relatively short - no more than five minutes' duration in a really dark, rural location, and probably only 10 to 30 seconds from a more typical observing site. With some DSLRs, the camera can be operated using a programmable timer attached to the shutter control to take repeated exposures one after the other for as long as required, provided the battery is fully-charged beforehand.

Such a set up, under good sky conditions, can capture meteors of magnitude 1 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.

Images of meteor tails may be emailed to meteor at britastro dot org.  Image labels should include the name of the imager and the date and time (UT) of the exposure.

This e-bulletin issued by:
John W. Mason, Director, BAA Meteor Section
2012 August 08