17/18 November 1999: The night of the Leonids

The 'Leonids' are small dust particles that enter the Earth's upper atmosph ere with very high velocities (about 70 km/s). They are the result of the E arth passing through the path of the debris cloud of the comet Tempel-Tuttl e. The meteor activity associated with Tempel-Tuttle is called a 'Leonid ev ent' because the meteors appear to be coming from the direction of the cons tellation Lee. There is evidence that this comet has created meteor showers and storms for more than 1000 years. Named after Ernst Tempel and Horace T uttle who first discovered it in 1865 and 1866, the comet has a nucleus abo ut 4 km in diameter and orbits the Sun with a period of just over 33 years. When at its nearest to the Sun, it also passes close to the Earth's orbit. The last perihelion passage of Tempel-Tuttle occurred on 28 February 1998. The Earth passed through that same region of space on 17/18 November 1999 and, because of the comet's recent presence, an increase in the amount of c ometary debris was indeed encountered.