Meteor Observing

History

Wednesday, August 12th 1998, will see the return to maximum of the best known meteor shower - the Perseids. Believed to be associated with Comet Swift-Tuttle 1862 III, the earliest record of this shower's activity appears in Chinese annals of 36 AD. The discovery of the shower is officially attributed to Quetelet who, in 1835, reported that there was a shower occurring in August that emanated from the constellation Perseus.

Giovanni Schiaparelli computed its orbit in 1867 and revealed the likelihood that these meteoroids were debris travelling in the orbit of Comet Swift-Tuttle 1862 III. With this in mind, many expected a marked increase in Perseid activity in the early 1980s, associated with the anticipated return of the comet, which has a period of roughly 120 years.

Activity did increase, and average hourly rates jumped from 65 meteors per hour (1966 - 1975) to over 90 per hour (1976 - 1983), with a high of 187 per hour in 1983.

Curiously enough, the comet itself was not rediscovered. Some observers believe that, with declining rates since 1983, the comet has probably passed through perihelion unobserved, and that the Perseids did indeed -peak in 1983.

There is another theory however, that the 1983 high was caused by whatever precipitated a sudden leap in 1839 to a maximum hourly rate of 160, some 20 years before the actual maximum occurred! If so, the best of the Perseids this century, maybe yet to come.

Meteor Observing

Meteor observing does not involve the use of special optical equipment, except perhaps, a pair of 7x50 binoculars, if available. It is an area of astronomy in which the amateur can contribute much, by observing recording and pooling results, to assess current activity levels of established meteor showers, and to search for other undiscovered streams.

Before the observing watch, gather everything you will need together, such as a deckchair/groundsheet, a pencil and paper, a red torch, a watch (preferably with a digital display), warm clothing (a sleeping bag is ideal), and a flask of some warm beverage.

The best time to observe is between midnight and dawn. This is because, during that time, an observer looking up at the sky is facing forward in the Earth's path around the Sun, and the front side of the Earth hits more meteors - just like the windscreen of a moving car hits more raindrops. If you can not observe during these hours, go out after darkness falls, and you should see several meteors per hour - weather permitting! Find a safe observing site with a view of the. north-eastern sky. Allow your eyes about 15 minutes to fully adapt to the dark conditions, settle down and orient yourself with the constellations.

Have your paper divided into the following sections: DATE, No., TIME, STREAM and SPORADIC. Under 'DATE', record the date on which the meteor was seen, bearing in mind that the date changes at midnight. Number the meteors seen under 'No.' as 1, 2, 3 etc. 'TIME' refers to the time, in hours and minutes, when the meteor was observed. Record this in Local Time. If the meteor appeared to come from the general direction of the radiant, place a tick under 'STREAM'. All other meteors are recorded as 'SPORADIC'. That is all that needs to be done.

Shower Information

The Perseid meteor shower commences its activity around July 23rd and continues, through the maximum on August 12/13 until about August 22nd. The Zenithal Hourly Rate typically reaches 80, although some years have been as low as 4 and as high as 200. The meteors tend to be very fast, with an average magnitude of 2.3, and about 45% leave persistent trains. The Moon will rise at 22:08 UT (23:08 BST) and will, at 20 days old, be waning gibbous (71% visible). This will increasingly cause problems as the night progresses - its light will reduce the number of stars (and meteors) visible, and so raise the limiting magnitude. The Perseids are, however, renowned for an abundance of bright meteors and fireballs, and appreciable numbers of them should still be easily observable.

I encourage you to go out on any of the above dates, even just to observe these beautiful spectacles.