Going for the Storm - to South Korea

A journey to the 2001 Leonid meteor storm's 2nd peak

For some early image processing experiments on my own pictures click on the image above!

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 and 23, 2001. Preliminary pictures added March 17, 2002 (German mirror only).

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.