Going for the Storm - to South Korea
A journey to the 2001 Leonid meteor storm's 2nd peak
It was an amazing sight: A newsstand at a rest area, near one of
South Korea's crowded highways, on November 20, 2001 - and
each of the five national newspapers had an astronomical
photograph on the front page above the fold! Pictured were the
night sky over whereever (deciphering the Korean alphabet was
one thing, understanding the text was another ...) - and several
bright meteors. Those were among the best multi-meteor
photographs I have seen (click
here
and here
for two more clips!), and to find them featured so
prominently on Korean broadsheets was no accident: It had been
in this country, just two nights ago, that the second Leonids
storm of 2001 could be observed under near-ideal geometrical
conditions. In the end, the weather had cooperated as well, and we
had been there for the show, as guests of the Bohyunsan Optical
Astronomy Observatory (BOAO), the most modern
astronomical
facility in South Korea.
It had been an amazing confluence of events that had brought
more than 20 amateur astronomers from several countries in
Europe and Asia to this spot, many of them top visual and video
meteor specialists and/or veterans of the legendary desert camp
in Jordan where we had, two years ago, witnessed the first meteor
storm since 1966 (a detailled report is here). A site with such a perfect
viewing geometry for the predicted main peak, combined with
good climate statistics, had not been evident for 2001, and for a
long time most German amateurs had been pondering
expeditions to Eastern China and Australia. But at the national
meeting of the meteor observers in early 2001 suddenly Korea
was on the map: decent geometry, good cloud stats, perfect
infrastructure (see the Cosmic
Mirror # 222 story 7) - and there would be a German-Korean
couple of meteor observers taking care of all the details.
It is to Mr Wiechell and Mrs Lee-Wiechell that we - the 17 from
Germany and Singapore who eventually signed up for the tour -
owe much of the success as well as ease of our expedition to: They
had made crucial contacts to the BOAO and gotten us the
unexpected and highy appreciated invitation to stay there for
three nights. And they had organized a highly concentrated tour
around much of South-Eastern S. Korea, exposing us to quite a
percentage of the most important cultural sights of this country.
Only briefly had we stopped in the vast metropolis of Seoul, where
the old, the new and the future Korea (the latter represented by
'Bladerunner'-like huge video screens on many highrise fronts)
are all wrapped into one. An unexpected astronomical
icing-on-the-cake: a clever old bowl-shaped sundial in Seoul's old
palace.
For the next few days we had taken residence in an almost-finished
nice little hotel near the Oksan Sowon (a Confucian Academy even known
to TIME
Magazine!) near Yeongchon - which featured a bewildering
assortment of Korean and Japanese cable TV channels but no
working restaurant yet. We could use the kitchen, though, for
somewhat Western-style breakfasts - but in the evenings we
always ended up in traditional Korean restaurants where one sits
on the floor and is offered countless dishes of exquisite (if
sometimes unidentifiable) specialities. As with most astronomical
expeditions we also quickly found out about the local beer (Hite), plus a most delicious 22% liqour
made from rice that they sell in PET bottles of up to 1.8 liters.
The 'spirits' were high accordingly each evening, though that would
not stop us from monitoring the growing brightness of comet C/2000
WM1 (LINEAR) in binoculars from the balcony every evening.
With rare exceptions, all nights and days were clear in mid-November,
and the travel guide books had not lied about this being
perhaps the
best time to travel in South Korea: While it's not
bitterly cold yet, the forests have taken on glowing colors. That is,
if you find them: South Korea has such a high population density
that there are houses, roads and (mostly rice) fields everywhere -
unless you head for the mountains. And that we did, with our big
bus that the Wiechells had chartered, together with a daring
driver: It's in the dense forests and mountains that one gets to see
the 'other' Korea, namely old Buddhist temples. We had time to
sample a number of them (sometimes full of exuberant school
children that found the rare presence of Western visitors
decidedly more interesting than the old buildings) and also two
so-called folk villages which are historical sites but inhabited by
real people.
In
Kyongju we even encountered the remains of an astronomical
observatory
from the 7th century: It's mainly the basic 'mount' of what may
have been sophisticated measuring devices installed on top of it.
Ah, and then there was the geodesic adventure we got ourselves
into: While driving around the countryside, it was noted that one
road passes quite close to a so-called confluence point where lines
of integer latitude and longitude intersect. There is a worldwide 'movement' to visit all these
points on solid ground - and the confluence point that we were
approaching hadn't been conquered yet. It was to be only 800
meters from the road, but then we learned the hard way what 800
m can mean: The confluence task force had to break through
thicker and thicker underwood while scaling a steep hill, balance
on a narrow dam and eventually enter a farm with barking dogs
(but no one around). The point
itself turned out to be rather accessible in a vineyard, but on
a different way back to the road we almost ended up in a garrison
...
On November 17th the time had come to retreat to the
BOAO,
located on the top of Mount Bohyun (the 'san' in the observatory
name means mountain). It is the most modern and the largest of
the three observatories operated by the Korea Astronomy
Observatory, founded only in 1996: The two main instruments
are a 1.8 meter reflector and an unusual Solar Optical Flare
Telescope (the control building of which would later serve as the
logistical center for the meteor video cameras). Add to that a
visitor center with a well-stocked gift shop (they have tiny
working planispheres as key chains!) that draws an astonishing
number of day visitors, despite the remote location of the BOAO
and the winding road leading up Bohyunsan. Of even more
interest to us was the main building, though: He we would sleep
(Korean-style on the heavily heated floor), eat (mainly the Korean
instant 'Ramen' soups we had brought along) - and have
around-the-clock access to the Internet through a really fast
connection (click here to read some of the
messages we sent from BOAO).
It was this perfect connection to the rest of the world that would
allow us to become part of the global adventure that the Leonids of
2001 had promised to be: Whichever of the four published models
of the activity profile (discussed in Cosmic Mirror # 230) was right, it
would not be possible to observe the whole event from just one
location, as the event was spread out over many hours. As the
models we had come to find more trustworthy were predicting a
distinct - and higher - second peak around 18:20 UTC on Nov. 18,
we were bound to miss the first one: While already dark, the Lion
and thus the radiant would still be way below the Korean horizon
at 10:00 UTC. (A word about the confusing timezones is in order
here: Korean Standard Time or KST is ahead 9 hours of
UTC while the U.S. East and West Coasts are behind 5 and
8 hours of UTC, respectively. Thus 10 UTC on Nov. 18
corresponds to 2 a.m. in CA, 5 a.m. in NY and 7 p.m. in Korea, while
18 UTC is 3 a.m. in Korea the next day.)
There were basically three ways to check remotely how the activity
profile developped: watch a TV picture of the constellation Orion
and meteors therein from the U.S. on NASA TV (that service apparently
worked but was not available to us), wait for excited messages on
various meteor-related mailing lists (those would be delayed
because people were observing, not typing :-) - or watch a real-time
meteor fluxometer experiment run by NASA in connection with
a new airborne campaign. There were indeed profiles building up
on the various screens, but a with factor of 10 difference between
data generated on the aircraft and data from Mount Lemon in
Arizona. While the origin of the (as it would turn out) erroneous
numbers from the plane hasn't been explained yet, the way the
Mt. Lemon plot was created has since been described: A number of
visual observers were entering their counts directly into a
computer, using special 'mice', and a rough ZHR (zenithal hourly
rate) was calculated in near-real time and put online.
How the Arizona plot went - a screenshot from 22:45 KST. Also available
are screen shots from
19:51,
20:40 and
21:00 KST
(plus a shot of the
front page)
as well as airplane data plots from
21:30 and
22:45 KST.
And here are Alice
Springs data (visual again) from the 2nd peak.
Sometimes the software seemed stuck but then the plot advanced
on our computer screens, half an Earth away from Arizona. And,
boy, did it take off, to eventually peak around a ZHR (or whatever
the computer was calculating) of over 2000. The peak seemed a bit
late (more like 11 UTC than the 10 or 10:30 UTC predicted), but
otherwise it was reason to rejoice: Even though more than 3 years
had gone by since the parent comet Tempe-Tuttle has passed the
Sun, there were still highly concentrated dust trails meeting the
Earth even now. (Even after the successful prediction of the 1999
storm there had still been prominent doubters of the 2001 storms; see
Nature of Nov. 25, 1999, p.333!) One of the four models
that had not predicted any distinct peak over the U.S. could
already be discounted. And, even more thrilling for us at BOAO,
there was now every chance for an even bigger storm than the
Americans had just seen over our place.
The satellite view of Korea on Nov. 18 - here is a
wider view.
But would we see it? Watching the weather trends over the last
week, be it on Korean or foreign internet sites or on TV, we had
always remained optimistic - all cloud patterns seems to stay
clear enough of the BOAO site. But, just hours before the Leo
radiant would rise and while we were still digesting the
observations from the U.S. (the first e-mails were now in,
confirming the general impression from the Mt. Lemon plot), we
had suddenly lost sight of the stars! The top of Mount Bohyun
was in the middle of a localized cloud, to small to show up on the
satellite pictures. At times we could see only for a few meters. The
cloud hovered around, sometimes letting thru a few stars, then
covering up everything again. It was a most bizarre atmosphere now,
almost comical ...
The fog would not go away tonight: That were the firm words of
Young-Beom
Jeon, an observer with the 1.8 meter telescope, an experienced
amateur astro (and art)
photographer
and our personal host at the BOAO. But, he said, in his experience
one would just have to drive down the mountain a few hundred
meters (there was no 'up' left anyway) to find clear skies, and he
confirmed his suspicion with a small scouting trip. Frantically (more
or less) we started to pack our gear, willing to go any extra mile
required for clear skies, and the engine of our bus was already
running warm. But at our set decision time of 23:30 KST the cloud had
disappeared mysteriously, and after some confused looking
around we decided to stay for the time being. The skies above us
were as perfect as before (with a limiting magnitude of 6.3 for
most), while near the horizon some light pollution - from squid
fisihing boats offshore! - was inevitable.
With midnight approaching phase one of our Leonids
spectacle could begin: As 8 hours earlier in the U.S. the first
indication of coming wonders was a barrage of so-called
Earthgrazers, wonderfully slow meteors travelling over much of
the sky. Those are Leonid meteoroids just scratching the upper
layers of the EarthUs atmosphere and not burning up in a fraction
of a second as ordinary meteors do. Some of them displayed
intermittent or terminal explosions, others just faded away after
having sped 100 degrees and more over the sky. Soon thereafter
the Lion's head appeared in the East and with it the more
ordinary meteors. The 2nd, our, peak was predicted for a
little after 3 a.m. KST (it was now already November 19th here),
and the meteor rate soon started to take off. There were two
effects driving it up simultaneousy: We (i.e. the Earth) were heading
more and more into a dust trail shed by Tempel-Tuttle in 1866,
and the radiant was climbing higher and higher, so that
we could actually see more and more of the particles entering the
atmosphere.
Here are my personal 5-minute plots w/o any corrections applied -
click here
for a larger version of this hand-drawn masterpiece. :-)
At first I was counting the meteors in 10-minute intervals
(around 1 a.m. KST = 16:00 UTC there were some 15 per 10
minutes), but at 2 a.m. I switched to 5-minute blocks. Not being a
seasoned visual meteor observer I refrained from trying to
estimate the magnitude of every meteor (as enough others on the
mountain were doing) but concentrated on counting. At 2:15 there
were already 30 Leonids in every 5-minute block, at 2:30 it were
45, at 2:45 more than 70, at 3 a.m. 85. Thus my personal,
uncorrected hourly rate (HR) was now at 1000: The Leonids were
storming again! And that was just the beginning: From 2:15-2:20 I
counted 118, from 2:20-2:25 another 91 and from 2:25-2:30 again
108 Leonids. The personal HR thus peaked at about 1500 near
18:22 UTC, but with the proper corrections for limiting magnitude
and esp. radiant elevation a Zenithal Hourly Rate of 3000 and
beyond is likely (and since, as an inexperienced meteor observer, I
tend to miss perhaps 30% of the shooting stars in my field of view, the
value may be closer to 4000). By 18:55 my HR was back to 1000
and the storm was coming to an end, at least
numberwise.
How did it measure up with the 1999
experience? The HR clearly could not top what we had
seen two years earlier over Jordan's desert: There an individual
observer could easily count 70 to 90 meteors per minute at the
peak, corresponding to an HR of 5000. Simple geometry played a
key role there: The radiant had been about as high as possible at
66 degrees elevation back then while in Korea we had about 42
degrees. Since there is a division by the sine of the elevation in the
HR-to-ZHR formula (plus corrections for the limiting magnitude
and obstructions), the Jordanian value had to be raised by only
10% to get the true value while the Korean number has to be
raised by 50%! The factor-of-2 difference in HR also corresponded
(at least to me personally) to a different »feeling« of
the meteor storm: In Korea I only rarely had the subjective
impression of racing towards the radiant or of meteors raining
out of that virtual spot, while this »rain of meteors«
feeling had been overwhelming in 1999.
The lower HR in 2001, however, came along with a much higher
mean magnitude of the meteors - and a much higher incidence of
fireballs than we had in 1999 (when there were hardly any)!
Before and especially after the peak in numbers, when the radiant
was higher, the fireballs took over! And while that wasn't a perfect
replay of the famous global »rain of fireballs« from
1998 either, when the fireballs had been even brighter (see this report from Mongolia), the
combination of a true meteor storm in numbers and the high
number of fireballs turned the Leonids of 2001 into yet another
show not to miss! With the fireballs also came back the persistent
trains, those »glowworms in the sky« left by
particularly bright ones, lingering at a hardly fading surface
brightness for sometimes many minutes. Watching those trains
in binoculars, being twisted by the upper atmosphere winds, was
an out-of-this-world experience that cost me a few of my 5-minute
counts (esp. between 4:20 and 4:50 KST), but what the heck ...
:-)
The fireball show continued all the way to and beyond the onset of
dawn at 5:50 KST - there were some still shooting around even as
the sky had brightened up considerably. What a night that had
been, with the first peak on the WWW, the cloud scare, the
Earthgrazers, the meteor storm, the fireballs and trains. Another
hour was spent by many posting first thoughts to
the world, before a colorful sunrise thru distant cloud banks ended the
night for good. The night before hadn't brought any advance notice of
what was to come (some rare grazers and fireballs aside), and the
following night would turn out even more ordinary (with more
Taurids than Leonids for most of the time). Have we to be thankful
to the handful of tireless theoreticians or what, whose
calculations had said: yes, there will be another storm, and you'll
have to travel to East Asia, sorry?! And isn't it a pity that there'll
be only one possible replay, next year and spoiled by the full
moon, for the coming almost 100 years? We'll probably go for it, too
(to Utah, maybe), and if just to say goodbye to the rarest of sky
spectacles, the Leonid meteor storms ...
Daniel Fischer
First version posted Nov. 27, links added Nov. 30 and Dec. 4, 2001.
More pictures will be added eventually!
A lot of links about the 2001 Leonids can be found in the
Cosmic Mirror # 230.
All links I've found related to the expedition discussed above are:
There is also a report (in French) by
Marlot from another Korean observatory at Sobaeksan.
