The Moonlit Leonids: Modest Meteor Shower Expected

When most people hear through the news media of an impending meteor shower, likely their first impression is of a sky filled with shooting stars pouring down through the sky like rain.  Such meteor storms have indeed occurred with the November Leonids, such as in 1833 and 1966 when meteor rates of tens of thousands per hour were observed. 

In more recent years, most notably 1999, 2001 and 2002, lesser Leonid displays of up to a few thousand meteors per hour took place. 

Those recent Leonid showers - and their accompanying hype - are still fresh in the minds of many.  So it is important to stress here at the outset that any suggestion of a spectacular meteor display in 2005 is, to put it mildly, overly optimistic. 

In fact, this year's Leonids, scheduled to peak on the morning of Nov. 17, are likely to be a big disappointment, partly because of the expected lack of any significant activity, but mainly because of the Moon which will be just past full, flooding the sky with its bright light. 

It is for this very reason that Robert Lunsford, a well-known meteor watcher in southern California, says he is downplaying this year's Leonid display.  Posting an E-mail message on the Meteorobs Internet Mailing List (http://www.meteorobs.org/), he recently wrote:

"While the Leonids are important I certainly would not advertise them as a major shower this year, especially to a newcomer to meteor observing, since the display will be weak and badly affected by the intense moonlight."

The Leonids are so named because the shower's radiant point, from where the meteors seem to fan out, is located within the constellation of Leo, the Lion. The meteors are caused by the Tempel-Tuttle comet, which sweeps through the inner solar system every 33 years.  Each time the comet passes closest to the Sun it leaves a "river of rubble" in its wake; a dense trail of dusty debris.  A meteor storm becomes possible if the Earth were to score a direct hit on a fresh dust trail ejected by the comet over the past couple of centuries. 

Comet crumbs

The 2005 Leonids are expected to show only low activity this year, with only one possible trail encounter. 

Russian meteor scientist, Mikhail Maslov points toward a very perturbed old dust trail, which was ejected, from the Tempel-Tuttle comet back in the year 1167 and is forecast to cross paths with the Earth this year.  Maslov was the first to point out this possible encounter, and other researchers have since confirmed it.  This encounter is expected to occur on Nov. 21, at around 01h GMT, which would place Europe, Africa and western Asia in the best position to see whatever activity might occur.  Rates, however, are still expected to be quite low, probably on the order of a dozen meteors an hour or less.  And that's not even factoring in the Moon's interference.

As already noted, the "traditional" peak for the Leonids is scheduled for the predawn hours of Nov. 17.  But the almost full Moon will be not too far away, shining within the constellation of Taurus, making observations very difficult. 

What to look for

Watching a meteor shower consists of lying back, looking up at the sky . . . and waiting.

In addition to this year's handicap of a bright Moon lighting up the sky, keep in mind that

any local light pollution or obstructions like tall trees or buildings will further reduce your making a meteor sighting.

Leo does not start coming fully into view until the after midnight hours, so that would be the best time to concentrate on looking for Leonids. Also, because the Leonids are moving along in their orbit around the Sun in a direction opposite to that of Earth, they slam into our atmosphere nearly head-on, resulting in the fastest meteor velocities possible: 45 miles/72 kilometers per second.  Such speeds tend to produce bright meteors, which leave long-lasting streaks or vapor trains in their wake. 

Still . . . a mighty Leonid fireball can be quite spectacular and bright enough to attract attention even in the bright moonlight.  But such outstandingly bright meteors are likely to be few and far between this year. 

So, the bottom line: If you plan to brave the chill of a mid-November morning, a moonlit sky and the prospects of catching a glimpse of only a few Leonids, you should get an award for perseverance.  Good Luck!  

Basic Sky Guides

• Astrophotography 101
• Sky Calendar & Moon Phases
• 10 Steps to Rewarding Stargazing
• Understanding the Ecliptic and the Zodiac
• False Dawn: All about the Zodiacal Light
• Reading Weather in the Sun, Moon and Stars
• How and Why the Night Sky Changes with the Seasons
• Night Sky Main Page: More Skywatching News & Features

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.