[Prev][Next][Index][Thread]

(meteorobs) Fwd: American Meteor Society Electronic Circular - Fall 1998



------- Forwarded Message

Date: Mon, 02 Nov 1998 16:51:39 -1000
To: meteors@serve.com
From: Jim Bedient <wh6ef@pixi.com>
Subject: AMS Electronic Circular - Fall 1998

                     The American Meteor Society, Ltd.
                            ELECTRONIC CIRCULAR
                           Issue #7...Fall, 1998
                             --------=======*

Contents of this issue:

     1.  DRACONIDS 1998
     2.  MESOSPHERE POTPOURRI  
     3.  SCIENTISTS ANNOUNCE PLAN TO GUIDE SATELLITE OPERATORS THROUGH
         METEOR STORM
     4.  SATELLITES MAY BE SHATTERED BY INVISIBLE METEORS
     5.  NO INVISIBLE METEORS SHOULD EXIST
     6.  METEOR SESSION AT THE EGS IN THE HAGUE, APRIL 1999 
     
-------======*

1.  DRACONIDS 1998

Rainer Arlt
Director, IMO Visual Commission
visual@imodot net

Two orbital periods after the 1985 Draconid outburst, expectations were
high for the night 1998 Oct 8-9.  An outburst with activity of ZHR>500
occurred over Asian longitudes on 1998 October 8, 13h-14h UT.  The
information is based on visual reports as given by Koseki (Japan, 21
observers), a detailed report by Osada (Japan), reports from Xing Ming and
Jin Zhu (China), a visual and video report by Jun-ichi Watanabe (Japan),
radar observations by Simek (Czech Republic), radio observations by
Ewen-Smith (Portugal) and Bus (the Netherlands).

Details of the reports are as follows; all UT times refer to 1998 October
8, save for the last period:

Report by Masahiro Koseki (Japan, visual):
------------------------------------------
Period(UT) ZHR  +- [standard deviation]
0900-1000   14   6 (ZHRs were reported
1000-1100   23  11  by Koseki)
1100-1200   61  43
1200-1300  147  55
1300-1400  371 243
1400-1500  174 123
1500-1600  121  72

Detailed report by Kazuhiro Osada (Japan, visual):
--------------------------------------------------
Period(UT) ZHR  +- [1/sqrt(n)]
1050-1130  154  33
1240-1250  901 144
1250-1300  867 144
1300-1310 1082 165
1310-1320 1265 183
1320-1330  968 164
1330-1340  640 136
1340-1350  442 123
1350-1400  575 144
1400-1410  457 132
1410-1420  323 114 radiant below 20deg henceforth
1420-1430  302 114
1430-1440  193 136

Report by Jin Zhu (China, visual):
----------------------------------
Period(UT) ZHR  +- [1/sqrt(n)]
1143-1227  230  45

Report by Jun-ichi Watanabe (Japa, visual-video):
-------------------------------------------------
1200-1330  ZHR>200
1300-1330  28 GIA on TV monitor with lm~6.0 and a
           field of view of 40deg x 20deg

Report by Zhou Xing Ming (China, visual):
-----------------------------------------
Period(UT) ZHR  +- [1/sqrt(n)]
1336-1421  562  53

Report by Milos Simek (Czech Republic, radar):
----------------------------------------------
1330       maximum of 400 events per hour at unfavourable
           radiant geometry

Report by Bev Ewen-Smith (Portugal, radio):
-------------------------------------------
    -1000  no enhancement
1000-1200  increase of short events (<10sec)
1200-1400  4 events (10-20sec) per minute
1400-1415  decrease of short events, a few very large events (1min)

Report by Eisse Peter Bus (the Netherlands, radio):
---------------------------------------------------
0700-0800   9  events >1sec
0800-0900  14
0900-1000  28
1000-1100  33
1100-1200  64
1200-1300  97  maximum suggested at 1245 UT
1300-1400  90
1400-1500  31

Report by Ilan Manulis (Israel, visual):
----------------------------------------
1541-1741  5-7 per hour, group observation
1741-1836  1-2 per hour, lm=5.5-6.0

European results (visual):
--------------------------
Period(UT) nGIA  ZHR
1715-1815   7    24  Helle Jaaniste (JAAHE), Estonia
1745-1818   2     6  Jurgen Rendtel (RENJU), Germany
1750-1821   4    15  Rainer Arlt (ARLRA), Germany
1818-1855   3     8  Jurgen Rendtel (RENJU)
1821-1853   2     7  Rainer Arlt (ARLRA)
1817-1913   7    12  Marco Langbroek (LANMA), the Netherlands
1833-1903   4    21  Ike Lysell (LYSAK), Sweden
1837-1926   4    10  Enrico Stomeo (STOEN), Italy
1855-1930   0     -  Jurgen Rendtel (RENJU)
1853-1931   0     -  Rainer Arlt (ARLRA)
1845-1945   7    40  Jaak Jaaniste (JAAJA), Estonia
1912-1926   0     -  Stephen McCann, UK
2010-2045   2    13  Erico Stomeo (STOEN)
2242-2247   0     -  Jurgen Rendtel (RENJU)
0250-0330   0     -  M. Linnolt, California, USA  [1998 Oct 9]

If not explicitely mentioned otherwise, ZHRs were calculated by myself with
r=2.0, alpha=262, delta=+54.  A high proportion of faint meteors were
reported during the peak; the ZHRs may thus be underestimated.  We can
conclude that the Draconid maximum occurred at lambda_sol=195.078+-0.010
degress (eq. 2000.0).
----
Rainer Arlt, 1998 Oct 9

[Editor's Note:  The Draconid maximum came somewhat earlier then most had
predicted.  About a month prior to the shower, however, Jurgen Rendtel of
IMO forwarded a prediction by E.A. Reznikov of South Ural University:

"The numerical investigation of the motion of meteoroids ejected from the
nucleus of the comet Giacobinni-Zinner is carried out.  Calculations have
shown that the ejected particles should be observed on October 8, 1998.
The calculated time of a maximum is October 8.55 UT.  The radiant of the
meteor shower has a right ascention 17.5 hours and a declination 56 degrees."

Reznikov therefore predicted the maximum would occur on October 8 at 13h
12m UTC; Arlt calculates that the actual maximum occurred at 13h 15m UTC,
+/- 15 minutes.]
-------======*

2.  MESOSPHERE POTPOURRI

Jim Bedient
AMS Electronic Information Coordinator
wh6ef@pixi.com

The last issue stimulated some interesting comments, and I'm always
receiving some tidbit or other in the daily e-mail.  That's one of the fun
things about meteor observing: many different and unusual things happen out
under the night sky.  I'm happy to read and share everone's comments here.

In response to Norm McLeod's comments on simultaneous meteors, Dr. Jiri
Borovicka of Ondrejov Observatory in the Czech Republic wrote:

"I just want to note that during the 1997 video observations of Leonids in
Chile, I recorded two Leonids of very similar brightness (mag about +3.5)
only 0.8 sec apart in a limited field of view of 20 degrees across. These
were two of only nine Leonids recorded during three hours of observations."

Typical meteor observation... long hours of boredom punctuated by a
moment's thrill!

James Smith, an AMS observer in Westfield, New Brunswick, notes:

"As far as simultaneous meteors go, I've rarely seen 2 at once and probably
only once when they came and went at the same instant. One instance was
July 21/22 when a Perseid and a Sporadic shared the sky together, the 2nd
one appearing and disappearing 1/10 of a second behind the Perseid, but
overlapping by 5 or 6 [tenths of a second], going in opposite directions."

Perseid time has been my own most likely time to see near-simultaneous
meteors.  Perseids seem often to come in 'packets', or groups of three or
four within a few seconds.  I've read of others having the same impression;
I don't recall ever reading a study of the issue.  If anyone knows of such
information, I'd appreciate hearing about it.

One drawback of visual meteor observation is varying perception among
observers.  A recent discussion on meteor color brought the following from
AMS observer Norm McLeod:

"Quite a few people see no color in meteors or stars.  Joan [McLeod] gets a
little star color but meteors have to be as bright as Jupiter for her to
see any color, and it's iffy even then.  I have almost 100% of my meteors
at +1m or brighter as colored (no matter how far away from central vision),
about 60% of the +2m's, and 10% of the  +3m's.  If I am looking at the
ground when a fireball occurs, I can still give the magnitude and color
just from the flash on the ground.  For a couple of years I also recorded
meteor color intensities on the following scale : 1 - subtle, like star
color ; 2 - moderate, like the strongest star or planet color; and 3 -
intense, like airplane lights.  I never tallied up the results, but a rough
impression is a breakdown of 20% subtle, 40% moderate, 40% intense."

Norm obviously has remarkable visual perception.  I personally will only
occasionally record color in a 2nd magnitude meteor, and maybe only 30% of
the time for 1st magnitude meteors.

Speaking of thrills, we are all waiting and hoping that the '98 Leonids
will produce a 1966-style storm.  In response to an earlier article about
meteor observing in China, Marco Langbroek of the Dutch Meteor Society
(DMS) wrote in to say:

"The group around Wu Pinxu mentioned in your circular is the group with
whom we cooperate in our joint Chinese-Dutch Leonid expedition 1998 to the
Qinghui Province. We will setup a multi-station photographic and video
network during the storm. And also conduct visual counts of course. The
expedition is a serious scientific expedition in which Purple Mountain
[Observatory] and the Dutch Meteor Society cooperate, under the wings of
our respective Academies of Science."

"From our contacts, we know that the Chinese have plans for a large network
covering a large part of the Chinese longitudes during the Leonids.
Clearly, they have a very large interest in the upcoming apparition."

As do we all - good luck to all observers going after the Leonid max in Asia!

Since the IS life after the Leonids, I was pleased to see the 1999 edition
of Alastair McBeath's annual opus, the IMO Meteor Shower Calendar, arriving
in my e-mail inbox.  This is an excellent planning tool for visual,
telescopic and photographic meteor observers.  A quick perusal shows lots
of opportunity for observing major showers in the dark of the moon next
year.  To get your copy, visit the IMO web site (http://www.imodot net/).

A note of interest to fireball researchers.  Marco Langbroek has reported a
source of possible daylight fireball reports:  Iridium flares!  Iridium
flares can easily reach magnitude -6 or -7 on center line, and are thus
quite visible in daylight.  Marco reports:

"Jos Nijland yesterday presented us a video taken by a relative, who is
studying at the cinematographic academy. He had to do a subject on 'moving
clouds', so he set up his video late june to film a blue sky with drifting
cumuli."

"On the video (that is a daylight picture, to be clear) by accident two
Iridium flares have been filmed 3 minutes apart. Jos initially thought
about possible daylight fireballs, but one look of us was enough to
identify it as Iridium flares.  No problem seeing them in the picture! They
took about 5-10 secs, the well known image of brightening and then fading
again, while moving slowly.  Very spectacular!  But a possible source of
confusion for 'fireball' reports."

Thanks for bringing that to our attention, Marco.  I have had several
nighttime fireball reports that were obviously Iridium flares, but I hadn't
thought of daylight flares creating false fireball reports.  A quick check
with IRIDFLAR or another similar piece of software will quickly reveal the
truth if there's a question.  

Thanks to all readers for your comments.  I welcome all notes and input on
the material presented here.  The more you write, the less you'll have to
read of what I write!   
-------======*

3.  SCIENTISTS ANNOUNCE PLAN TO GUIDE SATELLITE OPERATORS THROUGH METEOR STORM

Centre for Research in Earth and Space Technology
Toronto, Ontario

Toronto, October 7, 1998 -- A team of Canadian scientists working with the
Centre for Research in Earth and Space Technology (CRESTech) outlined today
a global operation aimed at safeguarding the world's 600-plus satellites as
they head into the first serious meteor threat of the modern space age on
November 17, 1998.

Though the risk of damage from the Leonids meteor storm is considered
slight, a number of international satellite operators, including those of
the United States Department of Defence, the European Space Agency and the
Canadian Space Agency, are working with CRESTech to reduce the odds of
impact from the natural space debris forming the comet trail into which
Earth will soon pass.  The Leonids are a swarm of metoroids that intercept
Earth's orbit to some degree every year, usually with little more fanfare
than a spectacular night of watching shooting stars.  This year, however,
the storm will reach levels not seen in over thirty years as Earth travels
directly into a path of interplanetary flotsam flung by the
four-kilometer-wide Comet Tempel-Tuttle. 

That last peak occurred in 1966, at a time when only a handful of small
scientific satellites were in operation.  Currently, there are estimated to
be well over 600 operational satellites in Earth's orbit, transmitting
signals 24 hours a day for services such as search-and-rescue,
entertainment broadcasts, telecommunications, as well as the
global-positioning system (GPS) used by commerce, transportation industries
and military forces, among others. 

"In the last 30 years, people in technologically advanced countries have
developed a strong dependence on a wide variety of satellite services,"
explains Peter Brown, the University of Western Ontario astronomer leading
the CRESTech science team.  "Unfortunately, if even one satellite was
disabled during the storm, it may not only be a multi-million dollar
disaster for its owners but may disrupt services for up to millions of
clients."

Peter Brown is organizing the Canadian science team providing the
hurricane-style forecast of the shower's activities to satellite operators
around the world during the peak night.  Clients include the United States
Space Command, the European Space Agency, the Canadian Space Agency,
Canada's Department of National Defence and several other government and
commercial organizations.

For more information, please contact:

Andre Bellefeuille
CRESTech Communications Manager
Office: (416) 665-5464, Cell phone: (416) 707-9120
email: andre@admin.crestechdot ca
-------======*

4.  SATELLITES MAY BE SHATTERED BY INVISIBLE METEORS

Robert Matthews
New Scientist
 
THE Leonid meteor storm that may light up the sky in Asia when it strikes
the Earth next month could pose a bigger threat to satellites than
astronomers had feared.
 
Every year, around mid-November, the Earth crosses the orbit of a comet
called Tempel-Tuttle and passes through debris the comet has shed. This
burns up in the upper atmosphere as a meteor shower.  Every 32 to 33 years,
the Earth runs into an especially dense cloud of debris, turning the shower
into a storm.  At the peak of the last storm, in 1966, the skies above
North America were lit up by 5000 meteors in just 20 minutes.
 
Astronomers are now bracing themselves for the next Leonid storm, predicted
to reach a peak around 17 November.  Communications and other satellites
could be threatened by the bombardment -- and both NASA and the Russian
Space Agency have postponed launches until the danger has passed.
 
No one knows just how bad the damage will be. For example, astronomers
can't predict with certainty exactly where the densest part of the debris
cloud is.  Now Duncan Steel, an astronomer with Spaceguard Australia in
Adelaide, has thrown another variable into the equation.  If his model of
the chemical composition of the Leonid meteors is correct, attempts to
observe the approaching meteors may detect only a few per cent of them.
 
Steel says that data gathered during the recent visits by comets Hale-Bopp
and Hyakutake reveal that the dust these comets gave off was rich in
volatile organic compounds.  If the same is true of the cometary debris
that forms the Leonids, most of the meteors may be invisible. This is
because if they are made of highly volatile material, many will burn up at
relatively low temperatures -- too low to leave behind glowing trails
detectable from the ground. Cool-burning meteors will also emit relatively
few electrons, and that will make them invisible to ground-based radars,
which can only spot electron-dense trails.
 
"If small meteoroids in storms are largely composed of organics, then none
of the data collected to date gives a realistic assessment of the hazard
level," says Steel, whose conclusions are published this week in the
journal Astronomy and Geophysics (vol 39, p 24).
 
Current estimates put the risk of a serious impact between a meteor and a
large satellite at about one in a thousand.  Steel says his study suggests
that this "seriously underestimates" the hazard.  "If I am right, the
economic loss caused by the Leonids may be immense," he says.
 
Other astronomers agree that the reliability of the storm predictions
depends crucially on the composition of the meteors.  "Steel's paper is
very interesting -- though whether it is actually correct is another
matter," says Iwan Williams of Queen Mary and Westfield College, London.
"We may know after the Leonids next month."
 
Steel's advice is not to rely too heavily on satellite communication and
navigation systems in the coming month.  "I would not depend for my life on
the Global Positioning System being fully functional on 18 November," he says.
-------======*

5. NO INVISIBLE METEORS SHOULD EXIST

Jiri Borovicka
Ondrejov Observatory
borovic@asudot cas.cz

I have not read Duncan Steel's article yet, but from what I know about the
meteor spectra I would say the following:
 
Yes, most of the luminosity of meteors in the visual light comes from the
lines of sodium, magnesium, iron and other inorganic elements. So,
hypothetical meteoroids composed only from the organic material would
certainly produce fainter meteors than "normal" meteoroids of the same
mass. On the other hand, I doubt that the organic meteors would be
completely invisible, especially if they were so fast as Leonids (71 km/s).
This is because:
 
- Organic material can produce radiation of molecules like
  CN, C_2, CH, OH.
 
- Fast meteors induce the atmosphere to radiate. Although
  bright lines of nitrogen and oxygen lie in the near-infrared,
  there are bright visible nitrogen bands.
 
- Even faint fast meteors often exhibit trains of duration
  of about 1 second produced by the forbidden oxygen line
  at 5577 A of atmospheric origin.
 
As far as I know, no spectra corresponding to organic meteoroids were
reported up to now, although they may have been simply discarded as "poor
spectra".  I agree that such meteoroids may exist and may be more abundant
in fresh cometary ejecta.  This is all the more reason to do careful faint
meteor spectroscopy during the forthcoming Leonid outburst, although this
may be too late for the satellites!  But as for the number of meteoroids, I
am not so optimistic.
-------======*

6.  METEOR SESSION AT THE EGS IN THE HAGUE, APRIL 1999

Detlef Koschny                      
European Space Agency
dkoschny@estec.esadot nl

The next meeting of the EGS, the European Geophysical Society, will take
place in The Hague in the Netherlands from 19-23 April 1999. Session PS8
will be on "Meteors and Meteor Swarms", convener is Klaus Scherer at the
Max-Planck-Institut for Aeronomy in Lindau, Germany, co-convenor is Peter
Jenniskens, NASA. The text in the EGS newsletter says:

"The new developments in observations and aerodynamics of meteors should be
presented. Special empahsis should be put onto the latest observations of
the Leonid shower during Novemnber 1998 which is expected to have a huge
meteor rate. First results from the international Leonid observation
campaign shall be available."

Also of interest to you might be PS7, Small Bodies and Dust, convener: G.
Schwehm, ESA.

Check the EGS web page for more info,

http://www.mpae.gwdgdot de/EGS/egsga/denhaag99/denhaag99.htm
-------======*

The Electronic Circular is published by the AMS about four times per year.
Contributions are welcome and may submitted by e-mail to wh6ef@pixi.com.
Subscription requests may be directed to the same address.

------- End of Forwarded Message

[Editor's Note: Permission is granted by the author to redistribute the
 AMS Electronic Circular freely, so long as it is properly attributed.]

To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html