Perseids 1996: Prospects (I)
Expected position of the 1996 Perseid peak (Marco Langbroek)


Within a few months we will experience a very favourable Perseid meteor maximum: it will be new moon on August 14! Below, some predictions on when a possible 'new' peak will occur, as well as information on the position of the main annual peak and other aspects of this coming return.

THE 'NEW' PEAK: AUGUST 12, 0:30 UT +- 1h

The Perseid stream has shown 'near comet type' meteor outbursts (see [2]) in 1991, 1992, 1993, 1994 and 1995, connected to perihelion passage of the parent comet P/Swift-Tuttle in 1992. With the exception of the 1993 outburst these outbursts lasted only short (<1.5 hours). The general trend seems to be a diminishing peak ZHR from 1991 onwards. The outbursts occured about 0.5 days before the regular annual stream maximum, but the peak positions of the outbursts showed variation in solar longitude.
We are not sure if there will again be an outburst coming return, but chances are certainly still good, though if it occurs it will not necessarily be very spectacular. A slight enhancement of rates, with some nice bright meteors, is very well possible. And who knows: with some luck, it might be even more than a 'slight enhancement'....
We have a pretty good idea on when an outburst might occur, if it occurs. The position of the peaks from 1991 to 1995 shows a nice pattern. Extrapo- lated, and with an eye to the patterning in recurrent outburst phenomena with other streams, we can expect it to occur near solar longitude 138.945 +- 0.5 degrees (B1950). This will be on August 12, 0:30 UT +- 1h.
This will be very favourable for western Europe, which will have the radiant high in the sky at that moment, and a completely dark sky without moon or twilight.
We strongly emphasize however, that observers should monitor a much broader time-window than that mentioned above. This is only a PREDIC- TION!!! Another reason to keep an eye open earlier and later that night (besides for the obvious fact of gathering data from the annual stream component, which is of course as important), is the suggestion by some that last years more than one peak might have been operational (see the December-issue of WGN).

THE ANNUAL MAXIMUM

The 'normal' annual maximum of the stream is located at solar longitude 139.49 +- 0.04 (B1950, [1]), which will be around 14h UT on August 12 this year.
Activity might be slightly above the average maximum ZHR of 84 +- 5 since we are experiencing a very deep minimum in solar activity at this moment. Variations in solar activity have it's influence on the upper atmosphere and introduce variations up to 20% in the annually observed rates of streams, most notably for streams consisting of fast meteors like the Perseids [1].
Due to the very favourable moon ephemeris, a large part of the Perseid activity curve will be observable from August 8 onwards this year. I wish all of you enjoyable observational nights!

Marco Langbroek (Dutch Meteor Society)
Jan Steenlaan 46
NL-2251 JH Voorschoten
The Netherlands



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Casper ter Kuile and Marco Langbroek