The mean orbit of the April Lyrids

In order to generate as complete a set as possible of meteors with well-determined orbits belonging to the April Lyrid meteor shower, a search was carried out of the International Astronomical Union Catalogue of Meteor Orbits held at Lund, as well as Dutch Meteor Society data and the Nippon Meteor Society data published in Asteroids Comets Meteors III and the World Wide Web pages. Meteors were required to have been observed between April 14 and 28 and have inclinations between 70° and 90°. Meteors were also eliminated if the right ascension and declination of the true radiant were more than about 10° away from the expected value. The Drummond D ' criterion was used on the set of meteors satisfying all the above conditions, so that meteors with a value of D ' in excess of 0.105, when compared to the mean orbit of the whole set of meteors, were eliminated. A new mean orbit was then determined, and the process was repeated in an iterative manner until a stable set of meteors was obtained and a new mean orbit for the April Lyrids, based on these meteors, determined. It is also suggested that the effects of Poynting-Robertson drag can be discerned within these meteor sets, and these considerations suggest an age of the order of 1.5 x 10⁶ yr for the April Lyrids.