The Leonid stream is composed of debris from periodic Comet Tempel-Tuttle, which has a period of precisely 33.18 years. Hence, when Earth passes through this part of the debris stream, we see a greater display of meteors than usual. Meteor showers each radiate from a specific area in the sky called the radiant, which is why they have the derivative names of the constellations. Thus, the Geminids emanate out of Gemini, the Perseids from Perseus, the Orionids from Orion and so on. The Leonid meteors appear to radiate from a particular area within the sickle-shaped head of Leo the Lion.
Observers see the most meteors when the shower's maximum occurs while the radiant is high overhead.
Unfortunately, these circumstances do not favor observers in the United States this year. The last optimal U.S. apparition of Leonid meteors occurred in November 1966, when observers across the central part of the country saw an estimated 150,000 meteors per hour. Prospects in 1999 Last year, the predicted storm didn't happen. True, the 1998 Leonids were more intense than usual, but there were no official counts of thousands of meteors. Most meteor observers put the number at peak closer to 200 to 250 an hour at best.