Why are the Leonids more intense some years than in other years?
Tempel-Tuttle orbits the Sun once every 33 years and last came by in February of 1998. Each time it passes close to the Sun it leaves a fresh trail of dust debris. Over centuries the dust trail will disperse and become part of the general Leonid shower. However, close to the comet, the dust will naturally be denser than in the rest of the debris ring, which actually consists of multiple dust trails, one for each of the last several comet passages (i.e., a 1966 dust trail, a 1933 dust trail, an 1899 dust trail). If the Earth intercepts one of the denser regions of the dust trail, a more intense meteor shower results.
