When the Leonid meteor shower strikes on the morning of November 18, 1999, our planet won't be the only place in the cross hairs. The Moon will also pass very close to the debris stream of comet Tempel-Tuttle. Some meteor enthusiasts think that there could be flashes of light on the Moon's surface each time a sizable Leonid meteoroid hits the ground. During the 1999 Leonid shower the phase of the Moon will be just 2 days past first quarter. That means the moon will visible in the night sky during the early evening on November 17, and approximately 35% of the lunar disk as seen from Earth will not be illuminated by sunlight. There will be plenty of dark lunar terrain where flashes might be visible.

On November 18, at 0h UT the lunar sub-Leonid point [the spot where Leonid meteoroids rain directly down on the Moon's surface] will be 9.4 degrees north of the lunar equator and 9.5 degrees sun ward of the day-night terminator. In other words, the greatest flux of Leonids are going to hit nearly dead center on the lunar disk as seen from Earth, just over the terminator on the sunlit side.