The nodal, the new and the old maximum of the Perseid meteor stream

Abstract

Visual observations of Perseid meteors carried out in 1953–83 at the Onsala Space Observatory are analyzed to study the fine structure of the Perseid meteor stream maximum. Observed hourly rates are corrected for weather conditions and to a zenithal value. The Perseid activity curve is studied (1) for all observed Perseids, (2) for Perseids of app. magnitude 2.0 or brighter. The activity curve for both data sets shows two main peaks, one at solar long. 138.65° (1950.0) , very near to the node of the parent comet (Swift–Tuttle) , and a second peak at 139.42°, corresponding to the traditional maximum of the shower. A third, less conspicuous peak at 138.96° is also evident in the data. This peak could possibly be an early indication of the so-called new maximum of the Perseid stream. The detection of a well-defined peak in rates very near to the node of the parent comet is important since the position of the Perseid visual maximum usually quoted in the literature deviates from the cometary node by almost 1° in solar longitude.