Dear friends Of Science and Astronomy,

Return of the Leonids - The timing favors western Europe, Africa, Brazil
and eastern parts of North America


On Sunday, Nov. 19th, Earth will pass through a stream of debris from
comet 55P/Tempel-Tuttle. The result: a shower of Leonid meteors.

"We expect an outburst of more than 100 Leonids per hour," says Bill
Cooke, the head of NASA's Meteoroid Environment Office in Huntsville, AL. This
pales in comparison to the Leonid storms of 2001 and 2002, when sky watchers saw
thousands of meteors. Even so, a hundred per hour would make the Leonids one of
the best showers of 2006.

Right: A Leonid meteor streaks past the Orion Nebula in 2001. Photo
Credit: Mark Brown of Alabama. [More]

The problem is, you have to be in the right place at the right time to see
them.

Earth's encounter with the comet dust is going to be brief-"possibly no
more than a few hours long," says Cooke. Forecasters differ on when the outburst
will occur. Estimates range from 0445 UT to 0630 UT on Nov. 19th (11:45 p.m. on
Nov. 18th to 1:30 am EST on Nov. 19th). The timing favors western Europe,
Africa, Brazil and eastern parts of North America: map.


Cooke urges observers to find the darkest possible skies. "These Leonids
are going to be faint." Why? "The stream contains very small grains of comet
dust. Small grains make faint meteors--it's as simple as that."

The mid-November region of Earth's orbit is littered with debris from
Comet Tempel-Tuttle. Every time the comet visits the inner solar system (once
every 33 years), it lays down a new stream of dust, pebbles and rock. This
creates a sort of "minefield" for Earth to navigate every November.

Not all of these debris streams are alike. For example: "A Leonid stream
we hit in 1998 was full of rock-sized debris. They made brilliant fireballs when
they hit the atmosphere," recalls Cooke. "The stream we're hitting this year is
just the opposite. It's mostly fine dust."

Right: A minefield of Leonid debris streams. The streams intersect the
plot at nearly right angles, so they resemble 2D clouds rather than 3D
filaments. Credit J. Vaubaillon. [More]

Debris streams are segregated-dusty vs. rocky-by the force of sunlight.
Consider the stream directly ahead of us: "It was ejected from the comet in
1933," says Cooke. "At first, the debris was a mixture of many sizes." But as
years passed, the smaller particles diverged from the larger ones. Radiation
pressure-the delicate pressure of sunlight itself-pushed the light dust onto a
collision course with Earth. Heavier rock-sized fragments resisted the pressure
and lagged behind.

Perhaps in some future year we'll encounter the larger debris from 1933
and receive an overdue display of fireballs. How would they get here? "Nudged by
Jupiter," suggests Cooke. Jupiter's gravity is strong enough to alter the course
of heavier fragments. Indeed, by guiding debris toward us, Jupiter is indirectly
responsible for many bright Leonid displays in the past.

But this is 2006. So prepare for an outburst of faint Leonids.

Extra: Don't believe everything you read. While meteor forecasters have
done a splendid job predicting Leonid outbursts in recent years-sometimes
"nailing the peak within minutes"-they could be wrong in 2006. The outburst
might happen at an unexpected time or it might be better than expected. Cooke
urges enthusiasts everywhere to keep an eye out for Leonid meteors the nights of
Nov. 17th - 19th. "The best time to look," he says, "is just before local dawn
when the constellation Leo is high in the sky."



By yours Dr.BHUDIA-Science Group Of INDIA.
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