2011 December 13

Geminid meteor shower nearing peak

The Geminid meteor shower is now underway, with peak activity expected during Wednesday, 14th December.  Unfortunately, weather forecasts indicate very variable observing conditions across the British Isles and Northern Europe, so it is important to have a good geographical spread of observers to ensure adequate coverage. The waning gibbous Moon will also be rather obtrusive, so observers are advised to direct their gaze away from the Moon, or to hide the Moon behind an obstruction such as the wall of a house.

The Geminids are currently the most active of the regular annual showers, with rates outstripping those of the Perseids for a 24-hour interval centred on their 14-15 December maximum – a real treat for observers prepared to brave the cold, damp and windy weather.

This year, Geminid activity is expected to peak at about 14h on Wednesday, December 14th, when the peak Geminid Zenithal Hourly Rate may reach 140 m/h – sadly during daylight hours for observers across Europe. The maximum is broad, however, and it is important to have a spread of observers making observations throughout the nights of 13th/14th December and on 14th/15th December to ensure adequate coverage of the shower maximum.  In addition, observations by BAA members in North America and the Far East will be welcomed by the Meteor Section to improve coverage of the period of peak shower activity.

The Geminid radiant (at RA 07h 32m  Dec +33o, just north of Castor) rises early on and reaches a respectable altitude well before midnight, so observers who are unable to stay up late can still contribute very useful watches. On the evening of Wednesday 14th December there is the added bonus of an increased proportional abundance of bright events after maximum; past observations show that bright Geminids become more numerous some hours after the rates have peaked, a consequence of particle-sorting in the meteor stream.

Geminid meteors enter the atmosphere at a relatively slow 35 km/sec, and thanks to their robust (presumably rocky/asteroidal as opposed to dusty/cometary) nature tend to last longer than most in luminous flight. Unlike swift Perseid or Orionid meteors, which last only a couple of tenths of a second, Geminids may be visible for a second or longer, sometimes appearing to fragment into a train of ‘blobs’. Their relatively low speed and the abundance of bright events makes the Geminids a prime target for imaging.

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