OCTOBER 17 Skywatchers around the world will anxiously look up during much of mid-November to see what this years version of the Leonid meteor shower will bring. In recent years the Leonids have produced some truly spectacular displays whose accompanying hype is still fresh in the minds of many.
Expert predictions suggest that at peak times this year, a meteor could streak across the sky every minute or two.
That means no meteor storms -- defined as more than 1,000 shooting stars per hour -- as in past years. A better bet, the forecasters say, is a Leonid performance equaling or possibly rivaling two other annually recurring meteor showers, the August Perseids and December Geminids.
This year's Leonids will offer an interesting twist, however. There will be not just one shower, but three. The first arrives Nov. 13 and the last is on Nov. 19. Skywatchers in nearly all locations on Earth will have a chance to see at least one of the showers.
In the early morning hours on days between the showers, a handful of extra meteors will grace the sky every hour.
Each shower will be visible from different locations. Only the side of the Earth facing the oncoming meteors -- as Earth scoops up space debris at the peak of a particular opportunity -- will get the best view. During a given burst, observers at other longitudes will see a very ordinary Leonid shower -- likely less than 10 shooting stars per hour -- by the time the rotating Earth turns them the right way.
Meteor showers are typically best viewed between midnight and dawn, when the side of the planet you stand on is heading into the debris stream. It's the same effect that puts more bugs on your car's front bumper than on the rear.
Meteoric minefields
The Leonids are so named because the showers radiant point, from where the meteors seem to fan out, is located within the constellation of Leo, the Lion.
The vaporizing bits streak all across the sky, though.
Leonids are caused by the comet Tempel-Tuttle, 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. Most of the debris is smaller than sand grains, with some reaching the size of a pea or marble.
The debris disintegrates in fiery flashes as it enters Earth's atmosphere.
A meteor storm becomes possible if the Earth scores a direct hit on a fresh dust trail ejected by the comet over the past couple of centuries.
"A minefield is a good analogy," says Bill Cooke of the Space Environments Team at the NASA Marshall Space Flight Center in Huntsville, Alabama. "Sometimes we get lucky and hit a dust trail, but more often than not we dont."
The dust trails spread out over time, however, as each particle continues to orbit the Sun on a trajectory similar to the path of the parent comet. So minor showers can result when Earth gets relatively near a trail's center.
Cooke recently issued his 2003 Leonid outlook, using data from several independent researchers. His assessment: "This year were going to brush past two dust trails. No direct hit is expected, but we still might see some nice displays."
The Leonids show will play out in three acts.
Act 1: Early opportunity
The first encounter -- unusually early for the annual Leonids -- is forecast to occur on Nov. 13 at 12:17 p.m. EST (17:17 GMT). Earth will pass within about 243,000 miles (393,000 kilometers) of a dust trail shed by Tempel-Tuttle in the year 1499.
| 
 Jay Ouellet put multiple exposures together to capture the activity of the Leonids in 2002 (above). Alejandro Bascolo photographed a colorful Leonid meteor last year.
|
| |
Skywatchers across western Asia, Indonesia and Australia are favored. Because of their proximity to the International Date Line, the shower will peak before sunrise on the morning of Nov. 14.
Under a dark, clear sky, a single observer in that part of the world might see 100 or more Leonids per hour, but unfortunately a gibbous Moon will also be shining brightly in the predawn sky and will interfere significantly, likely outshining many faint Leonid streaks.
Hourly rates are calculated based on 15-minute intervals. Peak activity does not necessarily last a full hour.
Act 2: Busy but faint
The second encounter is expected almost a full week later at 2:28 a.m. EST (7:28 GMT) on Nov. 19, when Earth will sweep to within about 33,000 miles (53,000 kilometers) of a trail of comet dust ejected in 1533.
Skywatchers across much of North America as well as northern and western portions of South America will be in the best position to see this display.
Meteor scientist Esko Lyytinen of Finland predicts a rate of 30 Leonids per hour during this second peak, while a forecast issued by Jeremie Vaubaillon of the Institut de Mecanique Celeste et de Calcul des Ephemerides in France suggests perhaps 100 or more per hour.
There is good news and bad news during Act 2.
The good news: The Moon will not be much of a hindrance, being in a thin crescent phase, just below Leo, near Jupiter. The bad news: Both Lyytinen and Vaubaillon believe that the majority of particles with this dust trail might be very small and hence the associated meteors may be only barely visible or perhaps not detectable at all with the unaided eye.
Meteor watching is best done, however, without any optical aids because the streaks come and go to quickly to be captured in binoculars or telescopes.
Act 3: The fireball shower
Perhaps the best bet for many observers will be when Earth passes through what's called "the Filament" by Peter Jenniskens at NASAs Ames Research Center and Hans Betlem of the Dutch Meteor Society.
| The Chronology of Events | | Several readers have asked about the sequence of the showers as presented here, suggesting that Act 3 should come before Act 2. Joe Rao explains why they're in the order he's placed them: The encounter with the dust trail from 1533 (Act 2) is likely to result in a brief, sharp peak, lasting no more than an hour or two. The Filament encounter (Act 3) involves material that is less concentrated -- more "spread out" in space. Peter Jenniskens of NASA has, in fact, pointed out that his predicted time of maximum activity has a margin of error of perhaps 0.7 day (nearly 17 hours)! | | | |
The Filament is a meteor stream consisting of the sum of many dust trails over many centuries, all having spread together so that individual trails are no longer recognizable.
The Filament could produce rates of about 50 per hour, or nearly one per minute, Jenniskens says, adding that the show will be "nearly like a Perseid shower, but more rich in bright meteors." In fact, Jenniskens is touting the Filament as "The Fireball Shower."
As with all predictions, these rates assume dark skies. City dwellers could see considerably reduced rates.
Act 3 could last about 24 hours -- very lengthy compared to Acts 1 and 2. The final production will be centered around 12:25 a.m. EST (5:25 GMT) on Nov. 19. This timing will highly favor western Africa and western Europe, though the northeastern United States and eastern Canada would also be rotating into a favorable position to see peak activity as well.
"My feeling is that the Filament should provide a pretty decent show," says Cooke. "We too [at NASA] will be watching. Its going to be an interesting year!"
| 
| Astronomy for the
Entire Family! Starry Night software brings the universe to your desktop. Map the sky from your location, or just sit back and let the cosmos come to you. LEARN MORE! | |
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.
advertisement
