Showdown in the Desert

The Leonid Storm of 1999:
How theory met reality at the Al Azraq meteor camp

As witnessed by Daniel Fischer, science writer,
Königswinter, Germany

Further stories & pictures from Al Azraq, Jordan, are on a special JAS page,
web pages by YK Chia, WGM and Jamshid and in a German article by G.Dittie.

More than 70 Leonid meteors are on the original negative
of this 10 min. exposure with a 24 mm lens at f/2.8 on
Ektapress 800 ASA that Eyad Mustafa took at the Al Azraq
desert camp around maximum time of the 1999 Leonid storm!
For image processing experiments on this picture click here!

New - some pictures taken by the author:
Before the Storm | The Storm! | After the Storm

A night to remember

Some had stopped counting alltogether now and were just gazing mesmerized at the sky on fire, others kept shouting frantically into their tape recorders, trying to preserve a permanent scientific record. But how do you cope with seven meteors flashing over all parts of the sky at the same instant, then another burst and another one? Whereever you looked now, be it close to the radiant in the sickle of Leo, be it at the North Celestial Pole or anywhere around the horizon, you didn't have to wait for more than a second, and there was another streak of light flashing through the sky.

Looking close to Leo, the constellation already high up in the sky, you could now really see the meteors streaming towards you from one spot - now you knew why scientists call it the "radiant". At times there would be several meteors 'radiating' there within a fraction of a second in different directions, forming a cosmic fireworks display. If you, on the other hand, looked far away from the radiant and close to the horizon, e.g. towards the Hyades, Pleijades and the setting planet Saturn, the meteors were flying downwards in parallel, almost like a curtain in front of the stellar canvas.

This was not a dream or a planetarium simulation. This was the real thing - seen, photographed and videotaped on the morning of November 18th, 1999, at the First International Astronomical Camp of the Jordanian Astronomial Society or JAS, at the former Hamzeh oil field deep inside Jordan's vast Eastern Desert near Al Azraq. The skies were just perfect here during all of this crucial night (and pretty good as well the nights before and after): A delay in the onset of the rainy season (that caused great concerns for Jordan's water supply) was a boon for astronomy.

An astronomical package tour, courtesy of JAS

Far from any human settlements, the only (minor) source of artificial light were lights on the border to Saudi Arabia, otherwise the sky was ours, with a zenithal limiting stellar magnitude of well above 6th mag. now. This place would have been a perfect setting for a November meteor outing in any case, with temperatures some degrees above freezing and no serious wind, but what the JAS had prepared here in terms of infrastructure was just incredible. The abandoned shacks and buildings of the oil site had been turned into an astronomer's paradise, with accomodation for 30+ people, a large kitchen and - although only intermittend - electrical power from Diesel generators.

And the Hamzeh (or Hamza) Astronomical Camp had been just the culmination of a week full of oriental hospitality the indefatigable members of the JAS had poured out over their guests from over a dozen countries on four continents. Initially the JAS had just planned to invite maybe 3 or 4 foreigners to join them for the occasion, but somehow the event had grown and grown - and now Jordan and the Al Azraq camp in particular had become one of the centers of the 'Leonid Universe', mentioned directly or indirectly ('50 astronomers freezing in the Jordanian desert') in most news reports about the meteor storm.

First there had been a two-day conference on the Leonids and meteors in general, taking place both at the impressive Al al-Bayt University near Al Mafraq - another oasis in the desert - and in Amman. The conference attendees enjoyed free accomonadation and full board at the luxurious Grand Palace Hotel there, which offered (via satellite TV) a bewildering glimpse into the culture of Jordan and its neighbors - and a breakfast, lunch and dinner buffet of fairy tale proportions and quality (already missed dearly by the author :-).

The conference also had a decidedly oriental flair, with royal salutes, Koran recitals and a surprise reception by HRH Prince Faisal, brother of King Abdullah, for the participants. Among the scientific highlights were detailled presentations by David Asher (Northern Ireland) and Robert McNaught (Australia) on their theoretical modelling of the Leonid dust trails, a model now to be tested within days - with both of its fathers present. There was Prof. Jack Baggaley, the president of IAU Commission Nr. 22 (Meteors and Interplanetary Dust), who reported in depth on his meteor radar work. And the author took the opportunity to once more advertise the recent lunar sodium tail discovery and to report on the 1998 Leonids expedition to Mongolia.

No trip to Jordan can come without touring the historical sites that abound in this part of the world, and the astronomers set out to visit Petra with its elaborate buildings carved out of limestone, the enormous Roman city of Jerash, and the old desert castles of Qasr al-Azraq, Qusair Amra (with perhaps the oldest 'planetarium' of the world, painted inside a dome) and Qasr al-Abd in the lush valley Wadi Seer. This latter "Castle of the Slave" also provided for the first 'Leonids' encounter as its walls are decorated by many detailled lion reliefs.

Off into the desert!

The real Leonids were waiting, though, and off the group went, heading due East (with two buses, in case one driver would chicken out - and indeed one refused to carry on when the road got bad!). By now we had gotten to know each other quite well - and the conference and camp attendees, most of them dedicated amateur astronomers, were truly 'United Nations'. Many Asian-Arabic countries were present (Syria, Palaestine, Jordan, Iraq, Saudi Arabia, the UAE), Iran, Armenia, Europe (UK, the Netherlands, Germany), Singapore, Australia, New Zealand and the U.S.

Jordan ist clearly one of the most "open" Arab countries (and its capital Amman, with an Internet Cafe at every other corner, could easily be somewhere in Southern Europe, save for the Arabic letters), and that view of the world easily transported to the conference & camp attendees. Who would have dreamt of Iraqis, Americans and Germans discussing computer image processing problems while walking through the ruins of Petra? Or Syrians, Iraqis and Iranians swapping eclipse stories and pictures? The August 1999 zone of totality had passed through these three countries, and observing camps had been erected in many places - with Iran's Esfahan creating a buzz just like they did in France and Germany. The sky conditions had been fine in the region, and the entries into an Iranian eclipse photo contest we were shown matched everything I had seen from European observers.

It was also deeply gratifying to find out first-hand that the apparent great 'cultural divide' between the Western world and the islamic region simply doesn't exist, at least among the astronomically minded. Just take Hani, a Jordanian now working in Saudi Arabia, whom we first encountered as an awesome Koran reciter with 20 years of experience and an expert on islamic cosmology - and who would soon be even better known for his practical jokes and humor. Or 20 year old Nada, who would, with equal expertise, host the royal reception, serve us donuts (from Dunkin Donuts, no kidding) in the midst of the Leonids storm - and turn out to be a "Simpsons" fan. Or Khalil Konsul, president of JAS, chairman of the Arab Union for Astronomy and Space Sciences and expert coordinator of the whole Leonids event: His diplomatic passport would speed up border affairs, while his mobile phone was usually ringing off the hook.

When the operation had finally moved into the desert site (where already many previous events had been held) on Nov. 16th, it definitely had the feel of an astronomical adventure camp, though for the somewhat grown-up. Surrounded by a vast flat stony and dusty desert populated only by a few Beduins and their livestock and home to only some oil fields, the Hamzeh camp was accessible only via a bad road, yet that wouldn't stop further members and friends of the JAS to come here, plus several journalists. There were Jordanian TV, a radio reporter from Germany, a complete team from the Associated Press, working for TV and print, and probably more, indistinguishable in the darkness.

Advance coverage by several news agencies stressing the ideal location of Jordan for the 1999 Leonids maximum, plus the high publicity JAS had gained over the years since its foundation in 1987, had already put Al Azraq "on the map". The cleverness with which JAS' members solve problems manifested itself soon enough when Khalil's crucial mobile phone ran out of power. In order to keep the communication with the AP people going (who heavily relied on the astronomers' advice), we literally had to break into a nearby oil field to commandeer its lonely - yet connected - telephone. The same locale, with its stable electric power, would become crucial again in the wee hours of November 18th when a video tape of the storm recorded by Georg Dittie with an image intensifier had to be copied for the AP team - they hadn't been able to get their own night vision equipment in time as it was needed in Baghdad...

Bracing for the encounter

The wait for the storm had been a long one, though. As usual, the observation had started a night early, to exercise all equipment, get a measure of the Leonid background rate (outside the discrete dust trails) and to be prepared for anything unexpected. The last time such an approach had been rewarded with the wondrous Asian-European rain of fireballs (which had been observed in Al Azraq under excellent conditions, by the way - one more reason to be here in 1999). Now the meteor activity stayed very low, 24 hours before the predicted maximum, and that was actually encouraging: The model calculations had also shown that the Earth wouldn't encounter the resonant cloud of old big dust particles again that had created the 1998 fireballs. It's so compact that the Earth passes through it only once per 33-year orbit of comet Tempel-Tuttle.

And so the first night was dominated not by Leonids but actually by Taurids, while the hourly rates of both streams hovered in the 10's. Although the (unseanonably mild) temperatures stayed several degrees above freezing, most observers eventually had to fight to stay awake til dawn (at 4:48 local time = 2:48 UTC). A smoldering charcoal fire and a water pipe (increasingly hip in the Arab world) helped a lot, though the Westerners weren't quite prepared to taste the latter - yet. Somehow the key JAS activists, namely their e-mail guru Mohammad Odeh, managed to connect a computer to the beforementioned phone line and to post the first observing results and comments to the world.

There had been some moderate Leonids hype in the world media and in Jordan as well, with predictions of several thousands of meteors an hour, but those were all based on wishful thinking, not hard science. Such high numbers were even given in an otherwise excellent "Sky at Night" program on the BBC that we all had watched together on the 15th, and numbers close to 10000/h were again mentioned in a front-page article of the Jordan Times of the 16th - our local experts, however, stuck to their just reduced prediction of 500 ... 1000 meteors an hour. Only the time was something everyone agreed on: Shortly after 2:00 UTC = 4 a.m. Jordanian time, the maximum would come.

The peak would just arrive half an hour before dawn, but with the radiant very high in the sky (and the Moon long set): That was why we had come here, sometimes half way around the world. The timing also meant that the geometrical conditions would improve continuously throughout the night. First Leo and the radiant would rise and the Moon would set, then the radiant would climb higher and higher, exposing us to an ever greater percentage of the meteors appearing in the Earth's atmosphere - and at the same time the meteor rate as such would also go up while the Earth raced towards its encounter with Tempel-Tuttle's dust trail from 1899. As we would not cross it close to the center (as was the case in 1966 during the legendary Leonids storm) the rate of meteors was in fact very hard to foretell. Everyone could just sit and wait.

Two bright Leonids, captured by Eyad Mustafa with
28 mm f/2.8, 10 min. exposure on Ektapress 800 ASA.

Here come the meteors ...

Already in the 1st hour after midnight Jordanian Time it was evident that the Leonids rate was much higher now than 24 hours ago. And there were also the first isolated cases of "persistent trains", those 'glowworms in the sky' left after the actual meteor is long gone. Here small binoculars come handy: First you notive a very narrow long greenish streak hanging in the sky (at an altitude of around 100 km actually, but that's impossible to guess). Then you notice how it expands and is deformed by winds in the upper atmosphere. The physics of the light emission is still somewhat mysterious, but a katalytic chemical process seems to be involved. Another nice train early in the night promptly produced the characteristic kink known so well from the famous 1998 fireballs. We were back in business!

In the 2nd hour of Nov. 18th, the Leonid rate for a single observer had now climbed to 1 per minute, although the elevation of the radiant was only 30 degrees - the real hourly rate (that someone directly underneath the radiant would see in principle) was already in the 100's. And still 3 hours to go until the predicted peak... 2:00 to 2:30 a.m.: The Leonids rate is increasing ever faster now - as is the number of their followers at our remote (?) desert camp. Car lights still line up on the horizon, along the only access road, fortunately not interfering with the observations.

There is also a remarkable acoustic background now: The JAS had installed a radio receiver tuned to an empty band on which a Turkish radio station well below the horizon was broadcasting. Normally there would be no way to hear the station, but whenever an ionization trail from a meteor appeared overhead in the right Northern direction, it would reflect the radio waves for a few seconds, and the radio would suddenly blare loud music over the camp site. This technique is particularly popular at the JAS - what a pity that a permanent breakdown of the power generator would silence it well before the maximum came. No other experiments were affected by the power failure, fortunately, as all cameras etc. ran on batteries.

Meanwhile the Leonids rate in the sky had grown so much that one started to get the feeling of actually racing towards the constellation Leo. Towards 3 a.m. the shower was already far more impressive than the strong Perseids of 1993 had been. The meteors now often came in pairs or triplets, travelling on nearly identical tracks, within sometimes less than one second. Soon the meteor rate for a single observer would surpass 5, then 10 a minute. The meteors were everywhere, regardless of whether you looked towards the radiant or anywhere else in the sky.

In the darkness I notice David Asher walking by. "I would say this is already part of the dust trail," he notes, shortly after 3 a.m., but "it's wider than the average width over the past 200 years, I think." 3:20 a.m.: Around this time the ZHR exceeds 1000 and will do so for the next 1 1/2 hours, a quick analysis of visual observations from many sites by the IMO will later show. And the rate rises and rises, while the sky quality remains excellent. Around Sirius, the sky is pitch-black, and the only significant source of 'light pollution' is the planet Venus, throwning on top of the zodiacal light pyramid - it helps to cover the brilliant planet with a water tower.

Hitting the peak, dead on time

Soon there are 7, then 13, then 27 meteors a minute - all counts for a single observer, of course, with his 110 degrees or so field of vision. Of course the temporal distribution of the meteors is irregular: Statistical fluctuations and perhaps real 'gusts' of activity bring several meteors per second in one time interval and leave gaps of several seconds without any meteor. But with the rate climbing on, those intervals get rarer. By now many are just marvelling at the rain of meteors while others count on - and Moh'd Odeh alone records up to 91 meteors in one minute (followed by 86 in the next minute, while before and after these 2 minutes the rate was in the 50's).

Returning to the - ongoing - global analysis, there was "a distinctive peak with a ZHR above 5000 on November 18, 2h04m +/-5m UT [...] It seems that the peak time of 2h08m UT predicted by Asher/McNaught is confirmed within a margin of at most a few minutes, observed activity is significantly higher. It is reasonable to conclude that the peak activity has been caused by the 3-revolutions old dust trail of 55P/Tempel-Tuttle. All observers who were able to view the peak under good sky conditions reported an abundance of faint meteors and a relative absence of fireballs. If this impression is real, taking it into account may result in ZHR values somewhat higher than those quoted below.

Ten minutes before the abovementioned peak time, at 1h53m +/- 5m UT [...], the ZHR profile shows a secondary peak with of ZHR of about 3500. [...] Asher and McNaught mentioned 1h53m UT as the nodal crossing time for the 1-revolution old trail, but did not expect activity from it. [...] Apart from the secondary peak mentioned above, the ZHR profile around the peak time looks remarkably smooth, even at the level of 5-minute intervals. However, observers in the French Provence report that, at the level of 1-minute intervals, additional minor peaks are visible between 1h30m UT and 2h30m UT. Whether these are significant will be one of the issues in a forthcoming detailed first global analysis." (IMO Shower Circular for the 1999 Leonids, 2nd Update of Nov. 20)

The numbers alone, 5000 or 3500 per hour, cannot convey the visual drama, however. It was better expressed by the frenetic shouting from some of the more enthusiastic Jordanian meteor counters - who still tried to record the brightness of individual meteors as well. Calls of "Wahat!" (1st magnitude), "Arba'a!" (4th) or "Chamzeh!" (5th) filled the air - the fainter meteors were now in the majority, any fireballs were missing, and there were only a few persistent trains of note. But the sheer number of meteors made more than up for their faintness (that was no problem anyhow for our dark site), and the maximum rate held for several minutes, with a marked decrease evident only after 4:15 a.m. (while the percentage of bright meteors increased somewhat).

At the end of this unforgettable night the most dedicated observers had counted around 3000 meteors, a Syrian with a mechanical counting device reported 3162 (that includes a number of Taurids and sporadics, however). Again Moh'd Odeh would be able to file a quick report through the internet, while the others in the camp could still hardly grasp what they had witnessed: the first undisputable meteor storm since 33 years and at least the 3rd-strongest of the century. With a ZHR of at least 5000 holding for several minutes, it fulfilled all storm criteria, regardless of whether you demanded 1000 meteors per hour or one every second.

A 15 minutes all-sky view by Eyad Mustafa
(note the zodiacal light pyramid around Venus).

Reality meets theory

At this morning, when some bright meteors were still shooting through the dawn skies, we didn't have such a detailled analysis, of course, but made simple extrapolations from our visual impressions. Still the ZHR values we extrapolated (5000-10000) would turn out to be much closer to reality than some values reported in the coming hours in the news media from 'official' sources. Neither the strange "1688 meteors per hour" figure attributed to NASA nor a value of 2200/hour out of Europe was correct: Once again even a small group of experienced visual observers had had a better grasp of a meteor shower's magnitude than some unproven hi-tech methods employed by big science organizations or even the space industry...

But what about the theory of the Leonid dust trails? By all accounts Asher and McNaught were "spot-on" with the predicted time of the maximum: They had indeed succeded in hitting the right time to +/- 5 minutes, and all of their skeptics expecting a later maximum (and therefore opting for observing sites much farther west) had lost. For once the media would be nice to the meteor astronomers that they had bashed (sometimes rightfully) so often in the past: The correct time was stressed in most stories I've seen so far, while the fact that Asher and McNaught had underestimated the strength of the maximum by a factor of ten was hardly mentioned.

What had gone wrong? The two had always stressed that predicting the ZHR was much harder than getting the time right. While the latter task mainly involved rigid celestial mechanics from first principles, the modelling of the particle density in the dust trails was an empirical challenge, based heaviliy on observing reports from the past. And here the problem must lie, McNaught told me on the morning after the storm: One simply cannot fit all the historical observations out Leonid outbursts and the ZHR of 5000 seen in 1999 with the same model. And that can, according to McNaught, only mean that many old reports underestimated the Leonid intensity!

Given the challenge that reliable counting presented for expert observers even during the comparatively moderate storm of 1999, one could well imagine that our predecessors of other decades (before 1966) and even centuries were way off in their assessment of the number of meteors in the sky. To figure this out will be a major task for the future. And what does the experience of 1999 mean for the Leonids in the coming few years? Do we have to increase the expected 10-25 thousand meteors an hour already predicted for 2001 and 2002 accordingly? The observations of 2000, which address the same dust trail (from 1866) that will hit us in 2001 and 2002, should be crucial and worthwile despite expected low rates and moonlight.

The fairy tale comes to an end

The Al Azraq observers (who would feature prominently in many news reports in the region, esp. on Jordanian TV, and even around the globe) had by now spent more than 10 hours out in the not exactly warm desert nights, and only a few would carry on with systematic observations for a third night. There are indications in the international data of "enhanced activity with ZHRs around or above 100 between November 18, 1500 UT and 2000 UT," according to the Nov. 20 IMO analysis - at this time the radiant was still below our horizon. "It is interesting to note that Emel'yanenko predicted a small secondary peak on November 18.7 UT due to an older duster trail" - in any case the big show was history, and even a few diehard observers got no more than 100 late Leos in 3 hours.

Eventually the camp site was cleaned and closed down on Nov. 19th, and the - by now rather dusty but overly happy - astronomers returned to civilization, i.e. the Amman hotel. Some would go on a quick trip to the Dead Sea (the lowest point on Earth) or visit buzzling downtown Amman on the following days, while our friends from JAS would bring along more data analyses from visual counts as well as the first pictures - which also went onto the JAS Leo'99 website (and some of which are 'quoted' in this article).

One by one the participants of this unique astronomical event had to leave Amman, and the remaining few would eventually meet on the evenings in a coffee shop, now even ready to try out the mysterious water pipe (that the Arabs call "Hubble Bubble", no kidding). We had made it through the Leonids storm of 1999, had been present at the very moment in space and time when a scientific theory was tested against the Universe (and when meteor forecasting matured to an exact science), and we had gotten to know and greatly appreciate a new world for all of us at the banks of the Jordan river - why would we be afraid of tasting every part of it...?

Dedicated to the incredible members of the JAS and those working behind the scenes who made it all happen.

Daniel Fischer

Drafted Nov. 18...22, first version posted Nov. 23, many links added Nov. 24...29,
picture pages added Dec. 2, 1999, header links updated Jan. 6, 2000.

Links for the Leonids of 1999

Pages with observational results of various kinds

Press Releases from various institutions

News stories of note on the storm

from Space.com, ABC, BBC (and links therein!), CNN (and links therein!), SPIEGEL (the upper picture is from Al Azraq - and doesn't show one meteor...), Space.com (on the balloon), Discovery, CCNet, Florida Today, RP, ExploreZone, SpaceViews, Astronomy Now, Ticker, CBS, MSNBC and ZDF-MSNBC, Florida Today and CSM (both on the Comet Chaser experiment), Space.com with a nice picture, and the Cosmic Mirror.

News collections are run by Space.Ref, Space.com, SpaceViews, Yahoo D and Yahoo USA.

News items on specific topics

The final predictions before the storm:
Armagh Page, an article by McNaught and another one on why all other models fail, a review (in German) by D. Fischer, stories from Discovery, RP and Space.com, and what ESA, the University of Bonn and CRESTech expected to happen.

Advance coverage of the JAS meeting & camp: A short AFP story is the 2nd item in this Space Daily page!!!

Fears for satellites / real-time surveillance:
AFPN on the airborne campaign, NASA Science News on a Leonid 'control center',
AFPN, RP, SpaceViews and ExploreZone on the risk for satellites,
a special page at STScI on Hubble and the Leonids.

Several Leonid hits on the Moon videographed!
A Special Page at IOTA and IAUC data;
early news coverage from NASA Science News, NASA HQ, BBC, Space.com, SpaceViews.

Homepages of Conference/Camp Participants

Various Pages about Jordan