12 November
On 12 November 1833, night was adorned with millions of meteors. Many noted that it seemed they originate from single spot in the sky, from the head of the constellation of Leo. This provoked further study of meteors in general, and it was decided that they will be given name from their apparent place of origin. Thus, Leonids, as that shower is now called now, had a major role in our understanding of meteors.
High meteor count like this one is called meteor storm. Although Leonids can be observed each year around 17 November, their numbers peek every 33 years. Though the last such peek was around the year 2000, they are pretty to watch every year, since they are quite bright and you can spot couple of dozens per hour anyway.