The Leonid meteor shower: why are there storms but no regular annual activity?

The Leonid meteor shower is the most famous meteor shower of all time. The main characteristics of the stream are well known, being very spectacular displays of meteors occurring on numerous occasions when the parent comet, 55P/Tempel-Tuttle, is close to perihelion. Since there is a perihelion passage of the comet due on 1998 February 28, it is a topic of intense interest to predict whether or not a spectacular display will be seen in 1998 or 1999. It is not, however, the primary purpose of this presentation to make predictions regarding this event, but rather to address an equally interesting problem related to the Leonids, which is: why do we not see even a moderate display like those of the Orionids or the Geminids in years when the parent comet is far from perihelion? We suggest that the gravitational perturbations from the planet Uranus, resulting from a particular set of geometrical circumstances that have been present over the last two thousand years, but which will come to an end in AD 2160, have been responsible.