Sky Talk November 2009: The Unpredictably Amazing Leonids

November and December feature two dramatically different annual displays of “shooting stars” — one always reliably intense and spectacular (see next month’s installment) and the other totally unpredictable and erratic in behavior. The latter is the Leonid Meteor Shower, famed for its amazing outbursts or “storms” in the past. Both displays happen under ideal conditions this year as far as interference from moonlight is concerned, their peaks occurring within a night or two of New Moon.

As November approaches each year, it’s common to hear longtime stargazers ask “Will the Lion roar again this year?” What they’re referring to is the utterly amazing and bizarre behavior of the famed Leonid Meteor Shower. It’s named for its host constellation of Leo the celestial lion, from which “shooting stars” appear to splash across the sky. Normal rates can range from as low as a disappointing 10 to 15 meteors per hour to as high as what happened in November of 1966 (and other times in previous years — especially 1833 and 1866, when the sky was so full of meteors that people thought the world was coming to an end!). As dawn approached here on the East Coast, the author saw a seeming blizzard of celestial “snowflakes” in the brightening sky. Further west under still dark skies (such as at the Kitt Peak National Observatory in Arizona), rates of 40 to 50 meteors per second were seen (and photographed), with some estimates placing the actual number at an astounding quarter million shooting stars per hour!

The Leonid storms themselves appear to come in 33 year intervals, with typically very low activity in the periods between. However, there have been surprising short-lived bursts where several hundred up to several thousand meteors per hour have been seen for a few hours on a number of occasions over the past decade, so you really never know what to expect. Then what about this year? Peak activity of at least 100 or more Leonids is scheduled to happen on the very early evening of November17th. Predictions from various sources give the maximum as occurring sometime between 5:00 and 6:00 p.m. EST (with some anticipating rates as high as 500 meteors per hour). Unfortunately, this is will be just after sunset for most readers. But as the sky darkens into the evening hours, you should still see a fine display of celestial fireworks.

The meteors will appear to radiate from the head of Leo, which looks like a backwards question mark and is known as the Sickle Asterism. Even though (as your Scientific Star and Planet Locator (#30092-27) will readily show) the constellation itself doesn’t clear the northeastern horizon until after midnight on the night of the shower, meteors will still be seen throughout the evening streaming from below the horizon. And as already mentioned, there will be no interference at all from moonlight this year. So if it’s clear on the 17th, be sure not to miss this year’s Leonids!

–James Mullaney
Former assistant editor at Sky & Telescope magazine and author of five books on stargazing.

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