November's annual Leonid meteor shower is associated with debris left behind during passages of Comet 55P/Tempel-Tuttle. Although this year's shower is expected to be unremarkable, there is a chance that short-lived outbursts could occur.

The 2007 shower may be unremarkable but it is notable for several reasons. First, it is expected to peak on a weekend night, making it easier for observers who like staying up late. The nominal predicted peak should occur on the night of Nov. 17 to Nov. 18.

Second, the moon gets out of the way before things get going. According to Sky & Telescope magazine, the best viewing "starts around midnight, when Leo rises." In Westminster, the moon cooperates, setting at 12:53 Sunday morning. The magazine says you will "likely see the most meteors 2-3 hours before sunrise."

The best way to increase the number of meteors you can expect to see during any shower is to observe from a dark sky site far away from interference from artificial outdoor lighting. This means traveling away from any nearby cities. The darker the sky is at your observing site the more meteors you will see.

Third, depending on which model you subscribe to, one or more outbursts may happen in which the expected hourly meteor rate spikes briefly. In his "Astronomical Calendar 2007," Guy Ottewell writes of a predicted outburst with a "zenithal hourly rate" (ZHR) of up to 200 meteors per hour between 11 p.m. Saturday and midnight.

Another outburst prediction is based on a model derived by Esko Lyytinen and Tom van Flandern. It was used to successfully predict an outburst in the 2006 Leonid shower. In a recent e-mail message to StarPoints, Mr. Lyytinen of Finland noted that he expects this outburst "to be quite weak" consisting primarily of "faint meteors" and fewer in number than last year's modest outburst of "only a few dozens" of meteors.

The underlying cause is that the Earth is expected to travel through debris left by Tempel-Tuttle during its 1932 passage. Unfortunately, this outburst is predicted to occur around 6 p.m. Nov. 18. Thus it won't be well suited for viewing from the United States.

Another outburst prediction by Russian Mikhail Maslov is based on a modified version of the Lyytinen-van Flandern model. It expects the surge to have a ZHR up to 60 to 65 meteors per hour.

The ZHR is an idealized rate with a technical meaning. It is the number of meteors that may be expected in one hour if the "radiant" - the point in the sky from which all meteors in a given shower appear to emanate from - was located at the observer's zenith (straight overhead) and viewed from a dark sky site free from light pollution. Of course, the radiant won't be that high in the sky, so the actual rate will be lower.