The comet Tempel-Tuttle (or more accurately, 55P/Tempel-Tuttle) was discovered independently by William Tempel in December 1865 and by Horace Tuttle in January 1866.

It was calculated that the comet had an elliptic orbit with a 33-year period. This information was then used to prove that Tempel-Tuttle was the same comet that had been observed by early astronomers in the year 1366 and again in 1699.

Most people consider Tempel-Tuttle to be an inherently faint and typically unspectacular comet that has only been observed on a few apparitions over the past 600 years. Its most recent apparition was in 1998, when it reached perihelion on February 28. As expected, it showed little activity, and only a small tail.

However, further inspection showed that this comet is more interesting than the first glance would suggest. Its orbit is oriented in such a way that the comet makes a relatively close approach to the Earth every few apparitions. And more importantly, the dust trail that the comet leaves behind is the origin of the annual Leonid meteor shower.