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(meteorobs) 2001 Leonids/IMO Press Release
I N T E R N A T I O N A L M E T E O R O R G A N I Z A T I O N
The 2001 Leonids
================
Dear Meteor Friend,
As you know, 2001 may well be the most exciting Leonid year in the
current epoch, with three major peaks, the first one visible from
America around 10 UT on November 18, and the other ones visible from
Eastern Asia and Australia around 18 UT on November 18 (morning of
November 19 local time).
For your information, we provide you in attachment with the following
documents:
1. Press Release;
2. Science Note.
It is not unlikely that your local press may ask you
for information about the upcoming Leonid event. For this purpose,
Documents 1 and 2 (a short press release and more expanded
elaboration) may be useful. Provided proper credits are given, you are
welcome to use these documents in any manner that suits you.
Finally, note that the International Meteor Organization is currently
making arrangements to ensure, weather permitting, that reliable first
results will be available within hours after the above times. Press
releases based on these results will also be forwarded to you.
Kind regards,
Marc Gyssens
Council Member
email: wgn@imodot net
phone: +32-477-64 05 48
I N T E R N A T I O N A L M E T E O R O R G A N I Z A T I O N
Press release
November 18: the day of the Leonid meteors
==========================================
From North and Central America, as well as from Eastern Asia and
Australia, people may see a lot of meteors - "shooting stars" -
between midnight and dawn of the nights of November 17 to 18 or 18 to
19, provided skies are clear. These meteors belong to the so-called
Leonid shower.
A first peak, visible from North and Central America, is expected
around 9:55 a.m. Greenwich Mean Time on November 18, which is 4:55
a.m. Eastern Standard Time. An activity equivalent to several hundreds
to over one thousand meteors per hour (or 10-15 meteors per minute) is
expected around the peak time.
A second and a third peak are visible from Eastern Asia and, mainly,
Western Australia, around 5:24 and 6:13 p.m. Greenwich Mean Time on
November 18, which is 1:24 and 2:13 a.m. on November 19. The weaker
first peaked is expected to flow over into the stronger second peak,
for which an activity equivalent to several thousand meteors per hour
(2 meteors per second!) is expected.
Notice that American observers should watch in the second part of the
night of November 17 to 18, while Asian and Australian observers
should watch in the second part of the night of November 18 to 19!
The International Meteor Organization, who collects meteor
observations world-wide for the purpose of analysis, wishes to point
the attention of the public to this spectacular natural phenomenon.
The Leonids are caused by a stream of predominantly very small
particles, less than 1 mm in size, which orbit the Sun with a period
of 33 years, together with their parent comet, Tempel-Tuttle. The
orbit of the Leonid particles happens to intersect the Earth's
orbit. Each year around November 18, when the Earth is at this
intersection, Leonid particles may enter the Earth's atmosphere and
cause meteors, popularly called "shooting stars." This year, the
Earth will pass through three dense dust trails ejected by the Comet,
in addition to several fainter ones.
As the predications above are based on models, peak times and peak
rates may vary somewhat from the ones quoted above. In particular,
there are indications that the first, American, peak may be stronger
than quoted here, whereas the second and third, Asian/Australian may
be weaker than quoted here.
Whereas Europe, Western Asia, and Africa will miss both storms,
observers there may still see several tens up to one hundred meteors
per hour in the second half of the nights of November 17 to 18 and 18
to 19.
Actually, Leonid meteors can be seen every year around November 17.
Along the larger part of Comet Tempel-Tuttle's orbit, however, Leonid
particles are scattered sparsely, so that, in most years, we see only
a few Leonid meteors per hour. Only in the vicinity of the Comet, the
density of Leonid particles is much higher. Therefore, we observe much
higher Leonid activity every 33 years during a couple of years, when
Comet Tempel-Tuttle revisits our region of the Solar System. In some
instances, we even see a real meteor storm!
Old chronicles contain references to past Leonid meteor storms back to
the 10th century A.D. The best-known Leonid meteor storms are those of
1833 and 1966, when tens of meteors per second darted across the
skies during the peak hour! The 1833 meteor storm was so spectacular
that it in fact launched meteor research as a branch of astronomy.
Since the 1966 meteor storm, Comet Tempel-Tuttle has completed another
revolution around the Sun. The passage of the Comet through its
closest point to the Sun on February 28, 1998 marked the beginning of
a five-year period (1998-2002) during which strongly increased Leonid
meteor activity is again possible.
Although 1998 gave us an unexpected (but meanwhile convincingly
explained) fireball shower, the first storm in the present Leonid
epoch occurred in 1999, with a peak activity around 60 meteors per
minute (yielding an equivalent hourly rate of almost 4000). In 2000,
no storm was seen, but several peaks with a few hundred meteors per
hour occurred. Observations in 1999 and 2000 matched the predictions
by astronomers David Asher and Robert McNaught really well, so that
there is more than good hope that the predictions for this year
are reliable, too.
In order to see meteors, the sky must be clear and the selected
observing site should preferentially be free of light pollution; the
less light, the more meteors will be seen! Notice that Leonid meteors
occur in the second half of the night. Hence, there is no point in
starting an observation much earlier. Die-hards who do not want to miss
anything of the show should then continue to watch until dawn. People
who cannot afford to stay up that long should focus on a period of, say,
one tot two hours centered around the predicted peak time for their
region.
Mind that it can be very cold in mid-November: warm clothing adapted
to the local climate is essential! For comfortable observing, use a
reclining chair, and install yourself in a suitable sleeping bag or
under several blankets. While observing, do not fix a particular star,
but look relaxedly and patiently to a wide area of sky and wait for
shooting stars to appear.
More information on the Leonids can be found in the International
Meteor Organization's bimonthly journal WGN and on the internet, at
http://www.imodot net and http://www.amsmeteors.org/imo-mirror.
For questions, contact Marc Gyssens at wgn@imodot net or +32-477-64 05 48.
Notice that the International Meteor Organization will send out a new
release with first results on the Leonids during the European early
morning hours of November 18, immediately after the event. All
recipients of the present release will automatically receive the new
release.
I N T E R N A T I O N A L M E T E O R O R G A N I Z A T I O N
Science Note
The Leonid Meteor Shower in 2001
================================
SUMMARY - From most of North and Central America, from Eastern Asia,
and from Western Australia, people may see a lot of meteors -
"shooting stars" - between midnight and dawn of the night of November
17 to 18 (America), respectively the night of November 18 to 19 (Asia
and Australia), provided skies are clear.
These meteors belong to the so-called Leonid shower. Three major peaks
are expected. The first one, visible from North and Central America,
occurs at 10 a.m. Greenwich Mean Time on November 18, which is 5
a.m. Eastern Standard Time. American observers may expect to see the
equivalent of several hundreds up to over one thousand meteors per
hour near the peak time. The second and third peak occur near 5:30 and
6:15 p.m. Greenwich Mean Time on November 18, which is 1:30 and 2:15
a.m. Chinese Standard Time on November 19. The activity of the first,
weaker, peak will flow over into that of the second, stronger one;
near the peak time, the equivalent of several thousand meteors per
hour is expected.
Europe, Africa, and Western Asia will miss both meteor storms;
however, observers there may still see from a few tens up to one
hundred Leonids per hour in the second half of the nights of November
17-18 and 18-19.
The International Meteor Organization, who collects meteor
observations world-wide for the purpose of analysis, wishes to point
the attention of the public to this spectacular natural phenomenon.
[Numbers between brackets refer to the glossary section.]
1. THE LEONIDS
-----------
The Leonids are caused by a stream of predominantly very small
particles, less than 1 mm in size, which orbit the Sun with a
period of 33 years, together with their parent comet (1),
Tempel-Tuttle. The orbit of the Leonid particles happens to
intersect the Earth's orbit. Each year around
November 17, when the Earth is at this intersection, Leonid
particles may enter the Earth's atmosphere and cause meteors (2).
Along the larger part of Comet Tempel-Tuttle's orbit, Leonid
particles are scattered sparsely, so that, in most years, we see
only a few Leonid meteors per hour. Only in the vicinity of the
Comet, the density of Leonid particles is much higher.
Consequently, every 33 years, during the years that Comet
Tempel-Tuttle revisits our region of the Solar System, much higher
Leonid activity is recorded. In some instances, this Leonid meteor
shower develops into a real meteor storm!
2. LEONIDS IN THE PAST
-------------------
Old chronicles from all over the world (European, Arab, Chinese,
Korean, Japanese, American, ...) contain references to past Leonid
meteor storms back to the 10th century A.D.
Well-documented observations of Leonid meteor storms
go back only to 1799, when the great German explorer and naturalist
Alexander Von Humboldt, rather coincidentally, witnessed a Leonid
meteor storm from Venezuela. The same spectacular phenomenon was
also observed from Florida.
However, the 1833 Leonid meteor storm had a far greater impact on
the public and the scientists alike, mainly because it was visible
in a much more densely populated area, namely New England.
At its peak, tens of meteors crossed the sky each second! Pious
Christians believed that Judgment Day had broken and many who
witness this celestial fireworks compared it to a snow storm!
Because of the interest it had sparked, this particular Leonid
meteor storm turned out to be very instrumental for the development
of meteor astronomy.
A somewhat less spectacular Leonid meteor storm occurred in 1866;
around 1899 and 1933, there was increased Leonid meteor activity,
but no storm.
In 1966, however, the Leonids returned in full splendor: observers
at Kitt Peak in Arizona saw a Leonid meteor storm peaking with
no less than approximately 40 meteors each second, which amounts
to a frequency of 150 000 meteors per second!
3. LEONIDS TODAY
-------------
Since the 1966 meteor storm, Comet Tempel-Tuttle has completed
another revolution around the Sun. The passage of the Comet through
its closest point to the Sun on February 28, 1998 marked the
beginning of a five-year period (1998-2002) during which strongly
increased Leonid meteor activity is again possible. Whether or not
a meteor storm actually materializes in any or all of these years
depends on several circumstances, on which we will briefly
elaborate.
4. WHEN DO STORMS MATERIALIZE?
---------------------------
Meteor showers (3) are caused by small particles orbiting the Sun,
in most cases released by comets. Each time a comet passes the Sun,
it releases "dust" particles (as well as gasses), in the case of
Comet Tempel-Tuttle every 33 years. As a first approximation, we may
compare this dust production to the condensation trail of a jet
plane. Like a condensation trail, a dust filament released by a
comet fades away over a period of a few centuries until it can no
longer be distinguished from the dust around the comet that was
released much longer ago. Only if the Earth passes through a dust
particle filament released by the comet at most 7 or 8 revolutions
ago, in the case of Comet Tempel-Tuttle less than about 250 years
ago, will a veritable meteor storm occur.
Every 33 years, when the Comet passes the Sun, there is a "window"
of about 5 years in which the Earth may pass through one or more
"young" dust particle filaments. When this happens, we see a storm
of between about one thousand and more than one hundred thousand
meteors per hour, lasting at most one hour. The actual peak of the
activity is often of even shorter duration. The precise frequency
depends on the age of the filament and whether the Earth goes
straight through the core of this filament, or only through its
outer regions. If the Earth misses all young dust particle
filaments, the older dust particles around the comet will give rise
to a more modest meteor shower producing 50 to 100 meteors per hour.
5. WHEN DO WE SEE LEONID METEORS?
------------------------------
Around November 18, Leonid particles may enter the Earth's
atmosphere from a direction - called the radiant (4) - located in the
head of the constellation of Leo, the Lion, from which the shower
derives its name. Because Leo is below the horizon in most of the
first half of the night, we can only see Leonids past midnight.
From one particular location, a possible Leonid meteor storm is
only visible if peak activity occurs between midnight and dawn.
In addition, you need a clear sky, which is not for granted
around mid-November ...
6. WHAT HAPPENED UP TO NOW?
------------------------
The current Leonid window was "opened" during the morning hours of
November 17, 1998, when early birds witnessed a veritable fireball
(1) storm: during a typical hour, 100 to 200 very bright meteors
appeared. These meteors were even so bright, that the spectacular
show could be followed well into dawn.
This fireball storm actually came as a complete surprise. The
embarassment it caused to scientists was an important incentive to
develop the current prediction model that proved very reliable up
to now.
In the morning hours of November 18, 1999, a veritable meteor storm
of up to 4000 meteors per hour (though much fainter than in 1998)
was witnessed mainly from Southern Europe and the Middle East.
For 2000, no storm was predicted. Several peaks of a few hundred
meteors per hour were observed, in reasonable accordance with
predictions.
7. WHAT MAY BE EXPECTED THIS YEAR?
-------------------------------
Scientists Robert McNaught and David Asher predict the following
peaks for November 18, 2001, all given in Greenwich Mean Time, also
known as Coordinated Universal Time (UTC):
Where to see When Expected activity
----------------------------------------------------------------
North and Central America 09:55 UTC 800 meteors/hour
(13 meteors/min)
East Asia/West Australia 17:24 UTC 2000 meteors/hour
(33 meteors/min)
18:13 UTC 8000 meteors/hour
(2 meteors/second)
The first peak is visible around 5 a.m. EST in the morning of
November 18 from North and Central America. Both other peaks
combined (it is not sure whether they can be distinguished) around
2 a.m. Chinese Standard Time in the morning of November 19.
Notice there may be minor differences between the real and
predicted peak times; also, the rates may vary. Similar models than
the one of Asher and McNaught tend to increase the rates expected
in America and to decrease the rates expected in Asia and Australia.
8. WHERE AND WHEN TO LOOK
----------------------
As explained above, you must be at the indicated region to see
a Leonid meteor storm this year. From America, you must watch in
the second half of the night of November 17 to 18; from Asia and
Australia, you must watch in the second half of the night of
November 18 to 19.
However, much is going to depend on the climate that is unstable
over many places in the world in that time of year. However,
climate is only what you expect, and weather is what you get!
Therefore, the best strategy to avoid bad weather is closely
following the weather charts and travel a few days in advance to the
location within your "action radius" that offers the most favorable
prospects.
Whether you choose to travel or stay at home, you will have to wait
and see until the last moment if weather conditions will be
favorable - a patch of clouds or a clearing at the right time can
create a world of difference!
Besides weather, light pollution is an important factor in choosing
an observing sight. Most Leonids are not that bright. The more
light pollution, the fewer meteors you will see! So, choose a dark
spot!
As explained above, Leonid meteors should be observed in the second
half of the night. Die-hards who do not want to miss anything of
the show should continue to watch until dawn. People who cannot
afford to stay up that long should focus on a period of one to two
hours around the predicted peak times.
9. HOW TO WATCH?
-------------
Mind that it can be very cold in mid-November: warm clothing
adapted to the local climate is essential!
Since you can never tell in advance at what precise time at which
direction in the sky a meteor will appear, you should never fix a
particular star, but rather patiently watch a wide area of sky in a
relaxed way until a meteor appears. It is not necessary to look in
the direction of the constellation of Leo: you will see meteors all
over the sky, in all directions.
For comfortable observing, use a reclining chair, and install
yourself in a suitable sleeping bag or under several blankets.
10.LEONIDS AFTER 2001
------------------
Two Leonid meteor storms may occur in 2002 as well, the first one
visible from European longitudes and the second one from American
longitudes. Activity may even be higher than in 2001.
Unfortunately, it will be Full Moon when these storms occur, in the
morning hours of November 19, and, therefore, a lot of the fainter
meteors may be lost to the moonlight. The best prospects for the
1998-2002 Leonid "window" are, therefore, for 2001.
GLOSSARY AND ADDITIONAL EXPLANATIONS
(1) COMETS - Comets are small celestial bodies (with a diameter
varying from a few kilometers to at most a few tens of kilometers)
that revolve around the Sun in long elliptical orbits.
Comets consist mainly of ice and dust. When a comet approaches the
Sun, part of the ice will evaporate and, because of the resulting
pressure, the gas will find its way through cracks and fissures in
the thin comet crest and be ejected under the form of "geysers."
The evaporated ice of these geysers will feed the coma and the tail
of the comet. Together with the evaporated ice, a lost of dust is
released. This dust eventually spreads along the entire orbit of
the comet, but remains densest in its immediate vicinity. Meteoroid
streams (4) usually consist of cometary dust.
(2) METEORS - Dust particles orbiting the Sun and capable of
"colliding" with the Earth are called meteoroids. Such a
meteoroid has usually the size of a sand grain or a tiny stone.
When it enters the atmosphere, with typical velocities of a few
tens of kilometers per second - several then thousands of
kilometers per hour! - not only the meteoroid but the surrounding
air experience enormous friction. This friction causes the air
surrounding the meteoroid to give light, in much the same way
as an electric current causes the gas in a TL lamp to give light.
Meteors typically light up at heights of 90 to 110 kilometers. The
resulting light is called a meteor or a shooting star. Usually,
the enormous friction causes a meteoroid to disintegrate into the
molecules it is composed of: the meteoroid "evaporates"
completely. Only the larger and stronger meteoroids may survive
traversing the atmosphere. The remainder of the meteoroid that
impacts on the Earth is called a meteorite. Leonids are too
fragile to produce meteorites, even if they are meter-sized.
Occasionally, meteors are exceptionally bright, brighter that the
brightest planets, and sometimes even brighter than to Moon. These
meteors are called fireballs.
(3) METEOROID STREAMS AND METEOR SHOWERS - The collection of particles
released by a comet (or comet-like asteroid) is called a meteoroid
stream. The meteor display in the sky caused by a meteoroid stream
is referred to as a meteor shower, or, in case of extremely high
activity, a meteor storm.
Meteoroid streams and their associated meteor showers are named
either after the comet from the particles originate, or, as is the
case for the Leonids, after the constellation in which its radiant
(4) is located.
The Leonids are not the only meteor shower we can see. In fact,
their are dozens of other meteor showers, but most of them never
produce more than a few meteors per hour. Two notable exceptions
are the Perseids, active around August 12, and the Geminids,
active around December 14. Every year, both showers produce
several tens of meteors per hour at their respective peak times.
Finally, we must mention that the Solar System contains a lot of
dust particles that do not belong to any particular meteoroid
stream. These particles cause so-called sporadic meteors, which
may appear any time.
(4) RADIANT - Meteoroids of the same stream (3) orbit the Sun along a
common orbit (roughly the orbit of the comet from which they
originate). When the Earth crosses a meteoroid stream, our planet
is "hit" by a "bombardment" of dust particles which all come
from the same direction. The perspective, however, leaves us the
impression that the meteor trajectories in the sky, when prolongated
backward, originate from a single point, just like the tracks of a
long, straight railroad. This point is called the radiant of the
meteor shower. Most meteor streams and showers are named after the
constellation in which this radiant is located. Even though the
backward prolongations of all meteors of the same shower intersect
the radiant, the meteors themselves can appear anywhere in the sky.
Hence, there is no need to look in the direction of the radiant to
observe a meteor shower.
To understand better what happens during a meteor shower, picture
the stream orbit as a "race track" along which all meteoroids race
the same speed. Picture the Earth, with yourself as an observer
on the Earth, as an "unexpected" obstacle on this race track with
which meteoroids may collide, producing meteors in the process.
If you look in the direction of the radiant, you will only see
short meteors, caused by meteoroids colliding with the Earth's
atmosphere while "running" almost straight toward you. If you look
at 90 degrees from the radiant, you will see long meteors, caused
by meteoroids colliding with the Earth's atmosphere just when they
were about to overtake you. If you watch even further away from
the radiant, you will again see shorter meteors, caused by
meteoroids colliding with the Earth's atmosphere after they had
passed you, and thus moving away from you.