From: Amara Graps (amara@amara.com)
Date: Tue Nov 16 1999 - 11:51:41 MST
Natasha Vita-More (natasha@natasha.cc) Mon, 15 Nov 1999 writes:
>The Leonid Meteor Shower will be returning this Wednesday and
>Thursday night. The Leonids are one of the falling stars of the
>meteor shower recurring annually in mid-November.
Yes, I'm looking forward to it, although the first snows arrived this
week, and it's cold!
Europeans should have a good view this time. (Southern Spain is
especially good)
Some friends and colleagues of mine at ESOC in Darmstadt
are involved in the tracking of the Leonids for ESA. They put
together this informative Web page for real-time meteor counts.
http://www.esoc.esa.de/pr/leonids.php3
On this web page, they will display real-time meteor counts from
three independent sources:
1) The counts from ESTEC scientists operating video cameras in
Southern Spain
2) The radar and optical data from the campaign organized by CRESTech
(Canada)
3) The counts made on-board a plane organized by Peter Jenniskens
(NASA-Ames)
I attach a press release that gives more information.
Amara
=================================================================
Royal Astronomical Society Press Notice
Date: 10 November 1999
For immediate release
Ref. PN 99/33
ISSUED BY:
Dr Jacqueline Mitton
RAS Press Officer
Office & home phone: Cambridge ((0)1223) 564914
FAX: Cambridge ((0)1223) 572892
E-mail: jmitton@dial.pipex.com
and
Peter Bond
RAS Press Officer (Space Science)
Phone: +44 (0)1483-268672
Fax: +44 (0)1483-274047
E-mail: 100604.1111@compuserve.com
RAS web: www.ras.org.uk/ras/press/press.htm
----------------------------------------------------------------------------
CONTACTS FOR THIS RELEASE
Professor Mark Bailey (meb@star.arm.ac.uk)
Armagh Observatory, College Hill, Armagh, BT61 9DG
Tel: 028-3752-2928, Fax: 028-3752-7174
Professor Iwan Williams (I.P.Williams@qmw.ac.uk)
Queen Mary and Westfield College, London.
Tel: 020-7882-5452, Fax: 020-8983-3522
MORE INFORMATION
on the Armagh Observatory Leonid web site:
http://www.arm.ac.uk/leonid/index.html
----------------------------------------------------------------------------
LOOK OUT FOR THE LEONID METEOR SHOWER
The 1999 Leonid meteor shower should produce a fine display in the early
hours of the 18th of November, Professor Mark Bailey of Armagh Observatory
will tell the Royal Astronomical Society's meeting on Friday 12th November.
Research done at Armagh, and by other experts around the world, suggests
that an unusually strong shower is on the cards this year when Earth passes
through streams of dust that have been shed by Comet Tempel-Tuttle.
Professor Bailey is putting his confidence in the work of his colleague
at Armagh, Dr David Asher, who collaborated with Rob McNaught of the
Australian National University. They believe they have discovered enough
about the location in space of the dust streams responsible for the meteors
to give 2.08 a.m. on 18th November, give or take 5 minutes, as the time for
the peak of the display.
The number of meteors is more difficult to assess. Dr Asher says, "It's
marginal as to whether the meteor activity will reach storm level in 1999,
but however strong it turns out to be, European longitudes are ideally
placed for observing the outburst". His best estimate is a maximum of 20
meteors a minute visible to a single observer in ideal conditions under a
clear, dark sky (conditions rarely experienced by casual observers).
Professor Iwan Williams of Queen Mary and Westfield College, London, who
has also done research on the Leonids, is more cautious, but said "Most
models lead us to expect a better display than last year". Neither Asher nor
Williams expects anything like the spectacular storm of 1966, when the rate
reached 40 a second for a brief period.
Professor Bailey comments, "It is sometimes said that comets are like
cats: they have tails and are unpredictable. If that's the case, predicting a
meteor storm has to be about as easy as herding cats! But Asher and McNaught
believe they have discovered how to do it. The 1999 Leonids will be a
serious test of their method."
Minimising the Danger to Satellites
A reliable method of predicting strong meteor showers such as the Leonids
has real practical value. The Leonids are the fastest of all meteors,
plunging into the Earth's upper atmosphere at 71 km/s -- 40 times the
speed of a rifle bullet. Despite their small size, the tremendous speed of
the Leonids means they pack a mighty punch.
Apart from knocking a spacecraft off alignment or causing physical damage,
such collisions can also generate a cloud of plasma which may cause
electrical shorts or damage a spacecraft's sensitive electronics.
This threat is not simply theoretical. In 1993, a European Space Agency
satellite called Olympus spun out of control, possibly as the result of an
electrical disturbance caused by the impact of a particle from the Perseid
meteor shower. There are currently more satellites in orbit around the Earth
than ever before, all of which pose a tempting target for one of nature's
miniature missiles.
Fortunately, impacts with spacecraft are quite rare, but satellite operators
around the world will be monitoring the situation very closely and taking a
variety of precautions.
"There could be a lot of activity, but we just don't know for sure," commented
Dr Walter Flury of the European Space Operations Centre (ESOC) at Darmstadt
in Germany. "It's better to take precautions now than be sorry later."
The European Space Agency's Space Science Department will provide
information on meteor numbers to ESOC every 15 minutes. Using this data
and radar counts from other sources, ESOC will be able to issue a security
alert, warning spacecraft operators to power down their spacecraft or turn
them away from the storm.
One of the largest targets, the NASA-ESA Hubble Space Telescope will be
manoeuvred so that its mirrors face away from the incoming meteors and its
solar arrays are aligned edge on to them during the Leonids' predicted peak.
Apart from reducing the exposed area of giant solar arrays, operators may
shut off power to vulnerable electrical components of satellites. In the
case of ESA's two European Remote Sensing (ERS) satellites, all of the
science instruments will be switched off during the peak of the Leonid
activity.
Even spacecraft located some distance from the Earth may be at risk. ESA's
Solar and Heliospheric Observatory (SOHO) studies the Sun from a vantage
point 1.5 million kilometres away, but it, too, will be turned so that its
main navigational aid, the star tracker, is pointing out of harm's way.
Expecting the unexpected
Since meteor showers -- the Leonids especially -- are given to springing
surprises, it will definitely be worth watching out on the nights of both
16/17 and 17/18 November, any time between 11 p.m. and dawn, though
after midnight is best.
Meteor watchers awaiting the Leonid shower last year (1998) were taken by
surprise when a spectacular display of bright meteors occurred 16 hours
before the predicted time for the maximum of the shower. However, the
explanation for this phenomenon was discovered afterwards by David Asher,
Mark Bailey, and Professor Vacheslav Emel'yanenko of South Ural University,
Chelyabinsk, Russia, and was published in April (see RAS Press Notice
99/09, http://www.ras.org.uk/ras/press/pn99-09.htm). They showed that
the bright meteors were seen when Earth passed through a dense arc-shaped
trail of particles shed from Comet Tempel-Tuttle in the year 1333.
NOTES
Meteors are caused by small fragments of material, mostly no larger than a
grain of sand, which burn up as they enter Earth's atmosphere at high speed
-- around 71 kilometres (45 miles) per second in the case of the Leonids.
Leonid meteors are dust particles that have come off Comet Tempel-Tuttle.
Most of this dust is still following the comet fairly closely in space. The
comet takes 33 years to complete an orbit around the Sun, and planet Earth
ploughs through its main dust trail when the comet returns to our vicinity
every 33 years. In the years when this happens, a strong shower or storm
takes place. Particularly intense storms were recorded in 1833, 1866 and
1966. In the years between returns of the comet, a very small number of
Leonid meteors are seen in mid-November.
Some meteor showers produce about the same rate of meteors around the
same date every year. Regular annual showers happen when the dust from
a comet has spread around the whole of the comet's orbit, something that
takes place gradually over a long period of time. An example is the Orionids,
a shower in late October each year caused by dust from Halley's Comet.
The Leonids are so-called because the trails of the meteors belonging to
the shower appear to radiate out from a point in the constellation Leo. But
this is an effect of perspective. In reality, the meteor particles enter the
atmosphere along parallel tracks from the same direction in space.
People who wish to observe the Leonids are recommended to wrap up in
warm clothes and find a cloud-free, dark site away from city lights,
preferably with a good view towards the north-eastern horizon. Between
about 11 p.m. and dawn, they can expect to see rapidly moving shooting
stars anywhere in the north-eastern sky, emanating from the 'sickle'
(a backwards question mark) made up by the stars in the head of the
constellation Leo.
--
Andrew Yee
ayee@nova.astro.utoronto.ca
***************************************************************
Amara Graps | Max-Planck-Institut fuer Kernphysik
Interplanetary Dust Group | Saupfercheckweg 1
+49-6221-516-543 | 69117 Heidelberg, GERMANY
Amara.Graps@mpi-hd.mpg.de * http://galileo.mpi-hd.mpg.de/~graps
***************************************************************
"Never fight an inanimate object." - P. J. O'Rourke
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