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Leonids: 2000

Beginning on November 16, I started posting summaries of Leonid activity to cover the periods of the predicted maximum rates on the 17th and 18th. Two important aspects of this stream are being looked for this year: confirmation of the model that successfully predicted the time of last year's great display and confirmation of one of several models being put forth to predict the actual rates of this year's display.

The Predictions

David J. Asher (United Kingdom) and Robert H. McNaught (Australia) apparently proved themselves last year when their model of Leonid activity successfully predicted the time of the meteor storm that occurred over Europe, but their predicted hourly rates fell short of the actual observations. Meanwhile, Esko Lyytinen (Finland) independently met with success when he also predicted the time of the European maximum AND predicted the high rates, but his success was lessened by the fact that he had predicted three maxima when only one occurred. So the question this year will be, "Which model will most successfully predict the time and rate of this year's display?"

The Asher-McNaught and Lyytinen models predict three maxima this year. These will occur as Earth passes very close to the meteoric debris released by the Leonid parent comet Tempel-Tuttle in 1932, 1733, and 1866. A new third model has been introduced by C. Göckel and R. Jehn (Germany) which also agrees with these models, although it does not consider material going back to 1733. All three models make their own predictions as to what the hourly rates will be, but the research of two other astronomers are also added at this point. Peter Jenniskens (California) and Joe Rao (New York) have taken the Asher-McNaught model and tried to improve on the hourly rate predictions. Jenniskens bases his predictions on the material gathered from the NASA/Air Force Leonid MAC mission of 1999, as well as ground-based observations throughout Europe. Rao's rate predictions are based on his extensive study of the historical observations of the Leonids.

Overall, there are three predicted aspects of the Leonids that will be tested this year:

• All three models predict the same times for encounters with three different dust trails. They will either all be correct or incorrect when the show is over.
• The Göckel-Jehn model predicts the display of November 17 could extend several hours before and after the main display, with several dramatic increases and decreases in activity.
• There are actually five different predictions for what the hourly rates will be this year. The basis of these predictions ranges from an analysis of last year's well-observed display to an analysis of the displays of the past couple hundred years.

As the Leonid activity progresses, I hope to point out how the observations compare with the predictions. I have also placed the pertinent details of each of the predictions below, so the readers will be able to watch, as observations are added, to see if the rates rise to the predicted maxima or not. When its all over, the winner in the prediction race should be obvious and, unlike the United States presidential race, there will be no recount at the end!

The Observations

November 15: The earliest Leonid report so far was by Vishnu Vardhan (India). He observed on November 15 from 21:05 to 23:05 UT. With Limiting Magnitudes (LM) improving from 5.6 to 5.9, he reported 5 Leonids the first hour and 6 during the second.

November 16: Christophe Marlot (France) reported 6 Leonids between 2:00 and 4:00 UT and then none from 4:00 to 5:30 UT. The brightest meteor was magnitude -2, while the faintest was 5. He reported a limiting magnitude (LM) of 5.7 for the entire period except the final half hour, when conditions marginally decreased to an LM of 5.5. Jin Zhu (China) observed from 18:43 to 21:03 (LM=4.8-4.9) and reported a total of 8 Leonids, two of which were brighter than magnitude 0 (-2 and -3). Ankur Puranik (India) looked for Leonids during the period of 20:30 to 22:30 on November 16 and saw only two. He pointed out that he was experiencing medium pollution levels and bright moonlight.

November 17: The Dutch Meteor Society has reported that observations by members split between two locations saw no enhanced Leonid activity during the period of 0:00 to 5:18 on November 17. This could be an early indication that the model of Göckel and Jehn is in error since they predicted an extended period of activity that would begin around 0:00 and see several peaks of 200 to 300 meteors per hour. In addition, it was pointed out that the observed Leonids were not particularly bright. On the other hand, just before 6:00 (about 15 minutes after twilight had officially begun) two Leonid fireballs appeared. One was estimated as magnitude -8, while the other was -10. Interestingly, a preliminary report from Birger Andresen (Norway) reports that two observers looked for meteors during the period of 3:30 to 6:00, with each detecting 30 to 50 Leonids (LM=5.8).

As the Leonid radiant rose above the horizon for most active observers on the east coast of the United States around 4:30 on November 17, clouds were more prevalent than meteors. The only eastern state experiencing clear skies was Florida, although there was a large gash in the clouds that was providing clear skies for some areas of southern Illinois, southern Indiana and Northern Kentucky, the southern portion of Ohio and the western portion of Pennsylvania.

Two reports are available from Florida. Janne Pyykko of Finland observed from 7:30 to 8:55 at Jupiter, Florida. He reports activity was definitely enhanced and reported 41 Leonids during the first hour, which covered the time of the predicted maximum. He made five-minute counts, and although most revealed 2 or 3 Leonids, his highest Leonid counts were made during the periods beginning at 8:10 (5), 8:15 (6), and 8:20 (5). He noted that he was only able to observe one-third of the sky and the moon kept the sky's limiting magnitude down to 3 or 4. Norman McLeod (Fort Myers, Florida) observed for three hours. He reported Leonid rates of 11 for the period of 5:26 to 6:26, 33 for the period of 6:26 to 7:26, and 13 for the period of 7:26 to 8:26. He added that his skies were quite good, in spite of the moonlight, with limiting magnitudes of 6.0 for the first two hours and 5.5 for the last hour. Interestingly, McLeod's numbers would tend to indicate a maximum much earlier than Pyykko's.

In lieu of additional visual observations, confirmation of high rates comes from two sources of radio meteor data. Pavel Koten (Ondrejov Observatory) has been monitoring the Leonids using backscatter radar. This system is capable of detecting meteors far fainter than what a visual observer could see, so that the numbers would be expected to be higher. His plot of the available measurements indicates Leonid rates first attained a 10-minute rate over 30 shortly after 2:00. During the next few hours the 10-minute rates fluctuated between 20 and 40. Shortly after 7:00 the 10-minute rates began climbing until they attained a peak of about 67 meteors around 7:45. After a slight drop during the next 10 minutes or so, the rates again turned upwards. Koten said almost identical local peaks occurred at 8:02 and 8:15, with the highest 10-minute count falling just short of 110. Rates had dropped back down to 30 per 10-minute period shortly before 9:30 and continued to drop thereafter. Michael Boschat (Nova Scotia) reported that mostly cloudy skies prevented his seeing any Leonids between 0:00 and 3:00; however, he routinely monitors meteor activity using radio equipment and reported hearing 19 meteors from 6:00 to 7:00, 103 from 7:00 to 8:00, 230 from 8:00 to 9:00, 108 from 9:00 to 10:00, and 33 from 10:00 to 11:00.

With no other east coast reports currently available so far, these observations indicate that the time of maximum occurred 25 to 30 minutes later than predicted. It would seem that the rate predictions of Joe Rao, Esko Lyytinen, and Peter Jenniskens were close to the actual rates. The Ondrejov peak at about 7:45 is certainly interesting, in that this would seem to confirm the Asher-McNaught and Esko Lyytinen time predictions. The large peak around 8:10, might be a continuation of the activity from the 1932 dust trail, perhaps adding some support to the Göckel-Jehn prediction of a somewhat long duration of activity from this trail, or it is something unexpected, like an older Leonid dust trail that was not considered in any of the model predictions.

The skies partially cleared for Wayne Hally (New Jersey), but not until after the time of the predicted maximum. Nevertheless, he observed from 9:00 to 10:45 (LM=4.3-4.5) and counted a total of 17 Leonids, indicating the high rates reported from Florida and Nova Scotia were now gone. The brightest meteor he saw was magnitude -2.

Not only was most of the east coast socked in by clouds, but much of the midwest was as well. The webmaster (Gary Kronk) watched the St. Louis weather forecasts of rain and possible snow for Thursday be proven wrong by mother nature as Thursday began as a crystal clear sunny day. These conditions persisted throughout the entire day--until sunset. A massive cloud bank moved in. It persisted throughout the nighttime hours (I checked about every 30 minutes), and the sky finally cleared about 30 minutes after sunrise Friday morning.

Reports have come in from the west coast of the United States. Robert Lunsford and Joseph Assmus drove to the Laguna Mountains, outside of San Diego, California to observe prior to moonrise (LM=6.1-6.2). Although the Leonid radiant had not yet risen at that time, they were hoping to catch the dramatic-looking atmosphere grazers--meteors that cut through the atmosphere at a tangent to Earth's surface and travel far across the sky. From 6:30 to 7:30 Joseph saw 4 Leonids, but from 7:30 to 8:30 he logged 12. Lunsford observed from 7:30 to 8:30 and saw 14 Leonids. Meanwhile, Wes Stone (Oregon) observed from 8:15 to 9:19 and saw 17 Leonids, and he observed from 9:20 to 10:24 and saw 12 Leonids. His limiting magnitude dropped from 6.0 to 5.8 during these periods. Dustin Brown (Washington) observed from 9:07 to 10:10 and logged 10 Leonids (LM=4.9), while from 10:30 to 11:23 he saw 5 Leonids (LM=4.5). These observations cover the period of maximum observed on the east coast, but it should be stressed that the Leonid radiant was then below the horizon, so only a small portion of the meteors would have been seen. Thus, the California and Oregon observations seem to confirm high rates, the rapid rise to maximum, and the rapid decline.

A report has now come out of Hawaii. Mike Linnolt observed off and on from 7:30 until 14:45. The limiting magnitude started out at 6.6, but dropped to 5.5 to 5.9 after moonrise. No Leonids were seen until his 8:58 to 9:33 session, when one was seen. The radiant position rose around 10:00 and the Leonids basically increased in number as the radiant climbed higher and higher into the sky. He saw 2 between 9:50 and 10:24, 3 between 10:40 and 11:13, 8 between 11:25 and 11:58, 10 between 12:45 and 13:18, 9 between 13:30 and 14:02, and 8 between 14:14 and 14:45. For clear skies, these numbers are about normal for the Leonids, so there was no trace of enhanced activity in this report.

It would seem that Earth has now completely exited the dust trail created by comet Tempel-Tuttle in 1932. The Leonids being observed now are basically debris from the numerous ancient dust trails that were released by the comet centuries ago. One question that needs to be answered is how fast do these dust trails disperse? We may soon get an idea as the dust trail from the 1733 return of the comet is crossing just ahead of our planet.

Observations are usually few and far between as the radiant moves across the skies of the Pacific Ocean. Following Hawaii, we can sometimes expect observations from northern Australia, and then many observations come out of Asia. Numerous observations have now come out of Xinglong Station in China. Huan Meng observed from 15:24 to 16:31 and saw 6 Leonids (LM=4.5). He then observed from 18:04 to 18:41 and saw an additional 6 Leonids (LM=5.0). Dan Xia observed from 16:04-17:25 and saw 7 Leonids (LM=5.8). Yuwei Fan observed from 17:00 to 18:30 and saw 20 Leonids (LM=5.3). Jing Zhong observed from 18:06 to 18:42 and saw 8 Leonids (LM=4.3-4.4). None of these observers reported a Leonid brighter than magnitude -3.

Arvind Parnajpye (India) reports that he observed from 20:10 to 20:55 and saw 3 Leonids (LM=4.0).

November 18: Large areas of Europe were experiencing cloud cover as the Leonid radiant rose above the horizon. Numerous reports have arrived United Kingdom, Norway, France, Germany, Italy, and Africa have cloudy skies. Nevertheless, many good reports have come out of the Middle East and Europe. A few of the more complete accounts are listed here:

• Alexei Pace (Malta) reported 6 Leonids from 1:12 to 1:22 (LM=5.7). He then reported 27 during the period of 1:22 to 1:43 (LM=5.7), 27 during the period of 1:43 to 2:00 (LM=5.7), and 23 during the period of 2:00 to 2:16 (LM=5.8).
• V’ctor R. Ruiz (Canary Islands) observed from 3:05 to 5:50. He had only one 5-minute count less than 10 and that came during 3:20-3:25 when 7 Leonids were seen. He had three periods when more than 20 Leonids were seen: 3:50-3:55 (21 Leonids), 5:10-5:15 (26), and 5:40-5:45 (31). The limiting magnitude was 5.9 to 6.1 for all but the final 5 minutes.
• Certainly deserving an honorable mention were several observers in Croatia, who battled 20% to 100% cloud cover for about 4 hours to see the Leonids. Tomislav Jurkic specifically reported he observed through holes in the clouds from 1:29 to 5:16 (LM=4.5). His only break during that period was from 3:11 to 3:33, when the sky became 100% cloudy. When holes again opened up at 3:34 he saw 17 Leonids in the next 14 minutes, his highest count of the morning.

There were also several reports from Arlene C. Brill (Turkey) indicating high numbers of meteors, but all of the details are not yet available. An email received at 2:22 indicated hourly rates were 50-80. An email update received at 2:53 indicated 30 meteors were seen in 20 minutes. Another update received at 3:55 indicated 57 meteors seen in a 30 minute session. These numbers are very preliminary, but if they are confirmed, they would indicate hourly rates significantly higher than those indicated by Asher and McNaught, but certainly in the ballpark of the prediction of Göckel and Jehn.

When magnitude estimates are available for individual meteors, it would seem this particular observed maximum had brighter meteors than the one on the 17th. A report from France indicated some fireballs in the -7 to -9 range. Fireballs were also mentioned in the report from Turkey, but no magnitude estimates were made. Ruiz also noted that between 5:10 and 5:15 he saw "bright meteors with persistent trains."

It is becoming obvious that hourly rates did not drop back to normal between the encounters with the 1733 dust trail and the 1866 dust trail. The following observations are from reports giving good breakdowns and good indications of sky conditions.

• Wayne T. Hally (New Jersey) began observing at 3:50 and saw 14 Leonids during the next two hours. He noticed the rates were on the increase, and began counting meteors at 15-minute intervals beginning at 6:06. From 6:06 to 6:21 he saw 10 Leonids, and rates steadily increased during the next half hour as 30 more were logged. He saw another 24 during the 15-minutes following 6:51. Hally registered his highest rates during the period of 7:06 to 7:51, when his three 15-minute counts revealed 28, 30, and 31 Leonids. His limiting magnitude was about 5 for most of the night.
• Michael Doyle (Virginia) began observations at 5:08 and saw 28 Leonids in the next hour. He watched rates steadily climb and began making counts for 20 and then 15-minute intervals. With a limiting magnitude of 5.7-5.8, his highest counts were 42 during 7:08 to 7:23, 39 from 7:23 to 7:38, and 33 from 7:38 to 7:53.
• Rafael Haag (Brazil) observed the display despite the fact that the radiant stays low for his southern latitude, with the highest altitude being 30 degrees at the end of his session. He reported 16 Leonids seen from 5:45 to 6:45 and 26 Leonids seen from 6:45 to 7:30 (LM=5.8-6.0).
• Pierre Martin (Ontario, Canada) observed from 6:31 to 9:01. His 5-minute counts steadily climbed and remained above 10 for the period of 7:01 to 8:11 (LM=5.98). His highest count came during the 7-minute period from 7:31 to 7:38 when he saw 32 Leonids.
• Felix Martinez (Virginia) began his continuous Leonid watch at 5:30. He observed 30 Leonids in the next hour (LM=6.1), 68 form 6:30 to 7:30 (LM=5.8), 34 from 7:30 to 8:30 (LM=5.2), and 51 from 8:30 to 9:30 (LM=5.5).
• John Krempasky (Maryland) observed from 7:00 to 8:20. He reported 82 Leonids during the first hour, with 23 seen during the 10-minute period of 7:20 to 7:30.
• Susan Delaney (Connecticutt) had her highest 10-minute totals during the periods of 7:30 to 7:40 (12 Leonids) and 7:40 to 7:50 (11 Leonids). The limiting magnitude was 4.7.

On the anecdotal side of things, Brian Stites, a pilot flying from Iceland to New York reported that between 5:00 and 6:00 he saw close to 100 meteors. He said this was his first true meteor shower experience and noted, "What a spectacular sight while over the ocean and void of any pollution or extraneous light."

These few east coast observations would seem to indicate that the zenithal hourly rate (ZHR) at maximum was well over 200 and maybe over 300--considerably higher than the Asher-McNaught and Jenniskens predictions.

From Illinois, I kept accurate counts from 7:50 to 9:10. I counted 47 Leonids in the first hour. My highest 10-minute count was from 7:50 to 8:00 when 11 Leonids were seen. My last two 10-minute periods produced the lowest counts of the night. My limiting magnitude remained at 5.5 throughout this session and none of my meteors exceeded Jupiter in brightness.

Details from the various radio and radar systems in operation have come in. At Ondrejov Observatory (Czech Republic) Petr Pridal observed both of the expected maxima on the 18th and noted that rates never really dropped off to normal Leonid values between them, possibly indicating the 1733 dust trail had dispersed to the point where it had partially bordered the 1866 dust trail. Beginning on November 17, he detected hourly totals of 60 at 23:30, and then for the 18th he reported an hourly total of about 130 at 00:30, 295 at 1:30, 290 at 2:30, 240 at 3:30, 230 at 4:30, 240 at 5:30, 310 at 6:30, 420 at 7:30, 320 at 8:30, and 140 at 9:30. Pridal adds, "Detailed minutes rates shows that the first peak occured at 3:38 UT and the second peak at 7:45 UT...In the time interval between 7:41 and 8:20 UT were detected 7 peaks with similar rates." Michael Boschat (Nova Scotia) monitored the radio waves for sounds of meteors, as on the night before. He had good covered of the third predicted maximum, where in the hour between 4:00 and 5:00 he detected 58 meteors, and between 5:00 and 6:00 he detected 128. A problem with the system caused him to miss the next hour, but between 7:00 and 8:00 he detected 219, between 8:00 and 9:00 he detected 149, and between 9:00 and 10:00 he detected 99. Once again, please remember that these are not observations of visual meteors, but frequently meteors which are not visible to the naked eye, especially at Ondrejov, where they estimate they detected meteors as faint as visual magnitude 9!

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