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

(meteorobs) The Leonids of 1998 - a first report live from Mongolia

The 1998 Leonids - the Mongolian View

How the major international expeditions near Ulaanbaatar fared


By Daniel Fischer, science writer, Koenigswinter, Germany
(currently in Ulaanbaatar, Mongolia)
 
Report posted Nov. 20, 1998, courtesy of the International School of UB
(Please respond directly to dfischer@astro.uni-bonndot de; do NOT use
 autoreply!)


About 30 professional and amateur meteor specialists from Canada, the
United States, Germany and several Eastern European countries have
followed the much anticipated 1998 activities of the Leonid
meteors for four consecutive nights from the Khurel Togoot observatory
10 km SE of the Mongolian capital Ulaanbaatar and from another site 50
km to the South. The sky conditions were mostly fine for the entire
interval (Nov. 15 to 18 UTC) and particularly excellent during the
night of  expected maximum activity (Nov. 17 UTC), with limiting
magnitudes for visual observers better than 6.0 - but temperatures
dropping to -30 degrees centigrade!

The highly unexpected development of the 1998 Leonids, with high
fireball activity way *before* the night of nodal crossing but no storm 
or even noticeable enhancement of activity around the crossing time is 
widely known by now - see e.g. the still evolving tabulation and ZHR 
plot at www.imodot net/news. The Mongolian observations (not included 
there at the time of this writing) were carried out by a high-profile 
joint Canadian-U.S. team led by Peter Brown (a grad student from 
Ontario Western University) and represented by Col. S.P. Worden of the 
U.S. Air Force, a 14-head German expedition (including the author) led 
by Juergen Rendtel, as well as several Slovakian and Croatian 
astronomers.

During the "maximum" night the Khurel Togoot observatory - normally a 
largely deserted place no longer maintained as an active astronomical 
research facility - was also host to a surprisingly large number of 
journalists called there by the Americans and Canadians. Most were 
international correspondents based in UB, but one had actually flown in 
from Canada. By pure coincidence a handful of bright meteors kept the 
spirits of the freezing crowd high just when Leo's head rose
around midnight Mongolian time (16:00 UTC on Nov. 17). But there would 
be no replay of the stunning fireball show from 20 hours ago: Mainly 
faint meteors could be spotted, and in particular no increase of the 
rate when the 'magical' time of nodal crossing (ca. 3:30 local time) 
approached.

At 2:20 Mongolian time (18:20 UTC) Col. Worden broke the bad news to 
the press: "We're not seeing any increase that would indicate we'll 
have a major storm in the next few hours," he stated and suggested that 
one might as well go home. "Do you have any idea what happened?"
someone inquired - Worden: "No!" But let there be no mistake: Last 
night's "very very strong bright shower of fireballs," according to 
Worden, "was probably one of the more impressive fireball shows on 
record." And he even referred to the German amateurs on the site: 
"Veteran meteor observers among both the German team and our team say 
that this is the most impressive fireball display they've ever seen." 
And for him personally - a solar astronomer by training - "that's
the most impressive thing I've ever seen in the sky."

Amazingly the fireball storm - if one chooses to call that rare 
phenomenon that - had been a global phenomenon: It had "persisted 
obviously for at least 18 hours, because we have reports from
across Europe and N. America, some of them visible in daylight - this 
is a very unusual situation," Worden summarized the first news that had 
reached him. (Even 3 days later the detailed activity  profile is 
unclear as may teams haven't had an opportunity to report their data 
in; it seems however that Europe got at least as high a rate as Eastern 
Asia, with ZHR values approaching 500.) 

A preponderance of fireballs long before nodal crossing is not exactly 
new, however, as Worden reminded the reporters: "1965 had a broad peak 
of very very bright meteors that lasted for 36 hours" - and was 
followed by a no-show at nodal crossing. 1966, however, had then 
brought a tremendous meteor storm at crossing time. For 1998 nearly all 
models had anticipated a profile similar to 1966, with a pronounced  
although much smaller -peak at nodal crossing. Why the forecasts failed 
so completely is now a major mystery. It only seems clear that the big 
particles that the Earth had encountered well before - but not during  
nodal crossing had been released by comet Tempel-Tuttle several hundred 
years ago. Since there were so many, Tempel-Tuttle must have 
experienced "a pretty major set of events" (Worden) back then. The
 small particles the Earth was encountering right now in contrast were 
young.

With these fresh insights into the vagaries of meteoritical science  
and its strong resemblance to long-term weather forecasting - swallowed 
with the help of a few free beers (courtesy of the U.S. embassy) most 
of the press had left by 3:30 a.m., leaving behind the astronomers on 
the observatory who had largely missed Worden's 'official' cancellation 
of the show. There were the Germans from the AKM (Arbeitskreis Meteore) 
who had largely gathered on an isolated rock and were recording the 
meteor activity with an array of video cameras with image intensifiers, 
photographic cameras and visually. Last night individual observers had 
seen up to 100 meteors in one hour, most of them very bright or 
fireballs, often leaving spectacular trains behind (this number, 
corrected for geometrical and other effects, corresponds to a ZHR
of about 250).

Now still some 35 to 40 meteors could be spotted in an hour, but the 
fireballs were largely gone, and the ZHR had clearly started to 
decline. And by the next night (18/19 Nov.) it would have
dropped off dramatically, to some 10 Leonids per hour. The observing 
logs, photographs (hopefully) and especially the roughly 100 hours of 
videotape from all 4 nights will be a major source for further studies, 
perhaps helping in the end to explain "what went wrong" or rather
why everything went so differently from the expectations this year.

Rather similar data material has been collected by the Canadian-U.S. 
expedition: Here, too, a battery of video cameras had been pointed at 
the sky, even from two sites (to get redundancy  plus 3D vectors for 
selected meteors), and visual counts had been made. But the highly
organized effort had had a second objective well beyond basic research: 
The visual counts as well as the data gleaned in real-time from one of 
the video cameras (by an experimental computer program, 'Meteorscan', 
as well as from someone watching a monitor) were telephoned every 15 
minutes to Canada. From there the information - now transformed to 
ZHR's  was eventually passed on to the Air Force's Space (Weather) 
Forecast Center in Colorado, which would have warned satellite 
operators in case of a real storm brewing.

None had been, of course, and no obvious satellite anomalies were 
reported either: The Mongolian experiment had mainly been a 
demonstration of principle. But interestingly the prolonged exposure to 
comparatively large meteoroids for 24 hours could in principle be as
harmful as a strong but short peak of activity. The further analysis of 
the Mongolian tapes and data in the coming months will help to quantify 
this possibility - and will hopefully lead to better predictions for 
the 1999 Leonids.

And the generally positive experience with the real-time analysis of 
meteor videos could one day lead to a world-wide network of automated 
monitoring stations - perhaps associated with an already existing 
network of U.S.A.F. telescopes keeping an eye on the Sun. The 1998
Leonids didn't live up to some peoples' expectations, no doubt, but 
they will eventually bring forward meteor science a great deal. And on 
an 'operational' level they have already made history.


A detailled expedition report will be announced next week at
http://www.geocities.com/CapeCanaveral/5599/mirror.html

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