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(meteorobs) Excerpts from "CCNet 115/2001 - 7 November 2001"
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From: Peiser Benny <B.J.Peiser@livjm.acdot uk>
To: cambridge-conference <cambridge-conference@livjm.acdot uk>
Subject: CCNet 115/2001 - 7 November 2001
Date: Wed, 7 Nov 2001 12:53:09 -0000
CCNet 115/2001 - 7 November 2001
================================
(1) LEONID METEOR STORM: WHEN, WHERE AND HOW TO WATCH
Space.com, 6 November 2001
[...]
(4) TUNGUSKA & OZONE DEPLETION
Jonathan Shanklin <jdsh@bas.acdot uk>
[...]
================
(1) LEONID METEOR STORM: WHEN, WHERE AND HOW TO WATCH
>From Space.com, 6 November 2001
http://www.space.com/scienceastronomy/astronomy/leonid_watching_011106-1.htm
l
By Heather Sparks
The Leonid meteor shower will flicker and flash above North America late on
Saturday, Nov. 17 through early Nov. 18. All you need to see it are your
eyes, a dark location, and a little weather luck. This and a few other
simple tips will assure a good view of the event, which experts say should
be spectacular this year.
The Leonid meteor shower is brought to us by comet Tempel-Tuttle, a ball of
ice and rock that orbits the Sun every 33 years, jettisoning tiny fragments
of itself. Each pass lays down a new trail of bits and pieces, or
meteoroids, which burn from the friction of the Earth's atmosphere as we
cross the Tempel-Tuttle trails every November.
The resulting meteors are popularly called shooting stars.
Tempel-Tuttle's path is slightly different each orbit, and the individual
debris streams spread out and drift through space. So each year the number
of shooting stars varies depending on which trails Earth passes through.
Forecasters say 2001 should provide the most spectacular show since 1966.
Several peaks of activity are expected in various parts of the world.
For North American skywatchers, Earth will enter the heavier parts of the
stream at about 11 p.m. EST on Saturday, Nov. 17. Activity will peak around
5 a.m. Sunday morning, when as many as 13 meteors per minute could be
visible, likely for a stretch of time that lasts less than 1 hour. The peak
corresponds to 4 a.m. CST, 3 a.m. MST and 2 a.m. PST.
Because this peak occurs near dawn on the East Coast, West Coast watchers
will have a longer period following the peak to look for meteors, said Bill
Cooke, a meteor forecaster at NASA's Marshall Space Flight Center.
The nights and early mornings surrounding the peak -- from Nov. 14-21 --
should also offer up a handful of meteors and possibly some meteor outbursts
as Earth potentially passes through various old debris streams.
Residents around the Pacific Rim may see a more intense storm. The heaviest
part of the debris stream is expected to slam into the atmosphere over the
western Pacific Ocean. Top viewing in Australia, Japan, eastern China and
the Philippines is expected to occur between 1:30 and 4:30 a.m., local time,
on Nov. 19. Rates during these peaks could approach two shooting stars every
second.
While Europeans will likely miss the strongest bursts, the Leonids should
still offer a decent shower there.
What you'll see
"The Leonids have a reoccurrence of heavy activity every thirty years or
so," said Dreyfuss Planetarium Astronomer Kevin Conod. Conditions are right,
he said, for Earth to pass through a dense stream this year.
Conod predicts the shower will flourish with 100 to 1,000 streaks and
flashes from different meteors throughout the night in North America. A
similar display should occur in Central America.
But like most meteor showers, the Leonids are notoriously difficult to
forecast.
"It's almost impossible to predict the exact number that will be seen at
this point," Conod said, comparing the challenge to another difficult
prognostication effort: "Weather forecasts don't tell you how many raindrops
are going to fall."
What you'll need
No serious equipment is needed for optimal viewing. Binoculars and
telescopes are of no use, because the shooting stars move across the sky too
fast. Your eyes are the only instruments you'll need.
The Leonids get their name from a point in the sky, called the radiant, from
which the shooting stars appear to emanate. The radiant is in the
constellation Leo, which rises in the eastern sky at night, getting higher
toward morning. But astronomers suggest looking almost anywhere but directly
at the radiant. Shooting stars will streak all across the sky.
The shower will be best in the early morning hours, so astronomers advise
getting up early rather than staying up late. It is in the early morning
that the radiant is high in your local sky, so more meteors are visible all
across the sky.
A cozy lawn chair or blanket to recline on will also prove helpful; without
one, all that looking up could put a strain on the neck. Warm clothing and
something hot to drink could prove wise, also.
Beyond that, the smartest planning involves getting away from bright lights
and cities. Light pollution has rendered much of the night sky void of stars
and can obscure much of the shower as well.
On the bright side, there will be no bright moonlight to drown out this
year's Leonids.
Where to go
Robert Lunsford, the Visual Program Coordinator of the American Meteor
Society, recommends getting as far into the country as possible. This will
help everyone, from astronomers to first-time viewers, watch and even
photograph the event. If you can't see many stars where you live, you won't
see many meteors, either.
If you live in a dense city, or a perennially foggy place, you might
consider planning ahead and booking a room at a remote bed and breakfast.
High mountainous areas will also provide better viewing because there's less
atmosphere up there to scatter light; more of the fainter meteors are
visible from high altitudes.
To get the full effect, find a dark location outside that's clear of trees.
Lunsford recommends allowing a half-hour for your eyes to adjust to the
darkness. Gradually you'll be able to see more and more stars as well as
meteors.
"The more stars you can see before the shower," said Lunsford, "the better
level of activity you'll see as well."
Earth will encounter another dense ribbon of the debris next November.
Europe and Africa are the favored locations for another predicted storm. But
a full Moon will dampen the 2002 show. After that, scientists say it will
likely be nearly a century before the Leonids storm again.
"It's now or never," said Robert Naeye, editor of Mercury, the magazine of
the Astronomical Society of the Pacific. "People should take advantage of
this year's Leonid storm, because astronomers don't think we'll see another
storm like this one until the year 2099. We will probably never see a better
meteor shower in our lifetimes."
Copyright 2001, Space.com
============================
* LETTERS TO THE MODERATOR *
============================
(4) TUNGUSKA & OZONE DEPLETION
>From Jonathan Shanklin <jdsh@bas.acdot uk>
It is true that there are reports that a dip in ozone levels is associated
with the Tunguska impact. What is not mentioned in association with these
reports is that at the time there was no global ozone monitoring network and
that what measurements there were, were highly unreliable. The measurements
in question were made using experimental data from stellar spectroscopy.
Early versions of the technique have errors of 50% or more, even when
designed to measure ozone and little real credence can be placed on the
claims from 1908. Claims that an ozone hole existed in the 1950s are based
on a similar technique that was used to measure ozone at the French Dumont
D'Urville station in Antarctica. Unfortunately when compared to
measurements made with the Dobson ozone spectrophotometer the evidence
disappears.
This is not to say that the Tunguska event didn't affect the ozone layer,
just that there is no conclusive evidence that it did.
Jonathan Shanklin
j.shanklin@bas.acdot uk
British Antarctic Survey, Cambridge, England
http://www.nerc-bas.acdot uk/public/icd/jds
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