Leonids 2000 : Information

DMS-members observing the Leonids 2000

    1. Rob McNaught
    2. Joe Rao
    3. Rainer Arlt
    4. Rob McNaught
    5. Joe Rao
    6. Rob McNaught
    7. Peter Jenniskens

Last updated: 23 october 2000

Rob McNaught

(12 february 2000)

Given that I'm very short of time at the moment, my response will be seen as most unsatisfactory, but I shall endevour to make a more detailed response in a couple of weeks or so.

Given that dust trails are clearly present in meteor streams, and that their geometry can only be determined with rigorous dynamical calculation it is impossible to predict the ZHR of a dust trail encounter without looking at the detailed geometry of the encounter.

Examination of the Leonid dust trail encounters makes it clear that missing the core of a young dust trail by about 20 Earth radii will result in rates lowered by about a factor of 100.

Each year the Earth goes through the region of the dust trails gives a lottery of which dust trail is encountered and how close. Each section of the many dust trails that could be encountered in any particular year, has a different age, density and mass distribution. To predict the ZHR using the dust trail theory required calculation of these quantities, but the most important part to be considered are

  1. What is the exact density profile of a dust trail? Theoretical approaches are very model dependent in this, so we just fitted Gaussians knowing that these were just a poor approximation to some of the factors involved (and we specifically stated this in the original publications).
  2. Knowledge of historical Leonid storm activity. For this we went with the independent and detailed analysis of Peter Brown. The historical record will contain many uncertainties but Brown's analysis is the most uniform of all available. Despite being unhappy with some of the values Brown derived (and he specifically noted that most of his results were lower limits), it would be unreasonable to pick and choose the data.

Given this, our simple semi-empirical model fitted all the historical data to the double Gaussian with only about 20% error. I don't try to hide from the fact that our 1999 predictions were too low by a factor of ~10. However, by rejecting only the 1833 ZHR, we can fit all the other storms (1866, 1867, 1869, 1966, 1999) with much the same accuracy. Only 1867 is discrepant by a factor of 3 and this fit makes Brown's 1833 ZHR too low by a factor of 2 (meaning 1833 and 1966 would have similar ZHRs by our model).

To reiterate:

My critique of other methods of storm prediction (including Ferrin's) was sent to this list in early November. The only other approach than dust trail modelling, that I see could work is the detailed dynamical modelling of the Leonid stream as a whole by Peter Brown and colleagues. The only current limitation with his study appears to be a lack of computer power. If the number of dust particles he integrates were to be increased by about a factor of 1,000 it would be possible to look at the integrated flux in a bin size much closer to the Earth rather than the 0.002 AU he is currently using. As stated above, dust trails vary in flux by a factor of ~100 over ~20 Earth radii (~0.0009 AU) in their radial profile, so a much smaller bin size than 0.0020 AU is required to prevent contamination by outlying dust trails that do not intersect the Earth. Given this extra computer power, I believe Brown's approach will be more valuable, in that it would not only include the dust trails (present by default without specific modelling of their profiles) but also the background. In other words, Brown's work will give a meaningful prediction in ANY year. The dust trail model looks only at storms and outbursts, which is a topic of specific interest, but cannot say anything about the background.

Cheers, Rob

Robert H. McNaught

Joe Rao

(4 october 2000)

In a message dated 9/29/00 12:58:51 PM Eastern Daylight Time, aakmp.antier@wanadoo.fr writes:

<< I wanted also to ask if there were more accurate estimations of the ZHR of the 2000 Leonids peak. Because if I refered to the NASA site it can be of 30 according to David Asher and Rob McNaught to 215 or 700 for Esko Lyytinen and Tom Van Flandern for the first peak at 7:50 or 7:51 UT, and it can be of 20 or 700 respectively for the second peak at 3:40 or 3:44 UT. So, I'd like to know if the analyse of the 1999 Leonids storm had permits to precise the estimations. >>

At last weekend's 10th annual Connecticut Star Party in Colebrook, I announced my own "take" on this year's Leonid shower. I think it is interesting to note that this year's display has a potential to be rather unique in the recent (modern) history of Leonid annals. At least within the past few hundred years, we have never had a scenario where very strong Leonid displays have occurred on consecutive nights. Perhaps the closest we've had to such a circumstance were the Leonids of 1961, when Perseid-type activity (ZHR = ~50) was noted by assiduous observers on November 16 and 17. As we all know, the most significant Leonid activity is usually confined to just one night.

In making an attempt to predict activity for 2000, I based my analysis on three past Leonid displays to which we have very good activity curves: 1866, 1966 and 1999. In the case of the first two I used Peter Brown's "Historical Visual Observations" article which appeared last year in Icarus. For the 1999 Leonids, IMO data published in the December 1999 WGN (27-6) was consulted. An attempt was then made to match the activity profiles and meteor trail encounter data provided by David Asher and Rob McNaught for these three cases with the upcoming situation in 2000.

For the morning of November 17, we should pass closest to material shed at the 1932 perihelion of 55P/Tempel-Tuttle at 07:53 UT, the distance between the Earth and trail separated by -0.00012 a.u. (the trail debris being located outside the Earth's orbit). According to the IMO's Global Analysis of 1999, we encountered this 1999 trail at 01:43 UT on November 18 of last year. This year, it would appear that we should again approach close enough for some sort of brief outburst or enhanced activity. I am thus suggesting a ZHR of 250 to 500 near the November 17, 07:53 UT time for this year.

For the morning of November 18, in deference to Major League Baseball, I am referring to this as "Leonid Wild Card Night."

On this night, two trails -- a 4 revolution and an 8 revolution trail -- with satisfactory ejection velocities may interact with the Earth. The 8-revolution trail, in fact, gave rise to the Leonid storm of 1866. The distances of these trails relative to our orbit are only a trifle greater than the 1999 value.

Unfortunately, as Asher and McNaught have pointed out, the 8 revolution trail (from 1733) has apparently undergone some perturbations due to previous close encounters with Earth. In addition, they also point to a case in 1801 regarding a 2-revolution trail with suitable ejection velocities that in many ways is rather similar to the circumstances regarding the 4-revolution trail in 2000. But no outburst or enhanced activity was reported in 1801 (over western Europe). The supposed 1801 enhanced activity would equally be larger than any nominal prediction that would be made for 2000. Such activity could certainly have been missed (although historical records from Armagh Observatory suggest otherwise), so good activity cannot be totally discounted in 2000. Unfortunately, the available circumstantial evidence looks against it, leaving open the possibility that our 4-revolution encounter in 2000 will also result in very little Leonid activity.

Interestingly, Emel'yanenko had predicted that in 1999, additional enhanced Leonid activity would occur on November 18, near 17:00 UT. Enhanced activity was indeed observed between 14:24 and 21:36 UT (according to IAUC 7313), with visual counts of 100-300/hr. The IMO indicated a "clear second outburst" of activity at 16:00 +/-1h UT, although observations made solely from China indicate a peak closer to 20:00 UT. What is important to note here is that this 20:00 time is within 5 minutes of the Earth's closest passage to the 4-revolution trail by Asher and McNaught. Unfortunately, Rob himself has indicated that the cut off for well-defined predictions regarding meteor trails seems to be at around a ZHR of 500 and the distance between last year's 4-revolution trail and Earth was a relatively large +0.0016 a.u. So there is some question as to whether any of the meteoroids encountered in 1999s secondary peak may have indeed been related at all to any cometary material shed in 1866. If so, it certainly would seem to enhance our chances for a significant display this year. Unfortunately, I do not have knowledge of what trail (or trails) Emel'yanenko was referring to when he made his prediction last year, but the 4-revolution (1866) trail is only one of several possibilities.

So far as what we might expect on the morning of November 18, I would thus suggest a rather broad range of possibilities. Since the 8-revolution trail will not be favorable for America as opposed to the 4-revolution trail, I only concerned myself with the latter.

It would appear that a projection of a ZHR of 20, as put forward by Asher and McNaught is certainly valid should a repeat of the 1801 disappointment recur this year. On the other hand, we could go to the opposite end of the spectrum and suggest that if everything properly fell into place, that a brief outburst with ZHR's as high as 1,400 to 2,800 (the most extreme limits) could also be possible near the trail encounter time of 07:51 UT as well!

With some "guarded optimism," however, I might suggest that the actual truth could ultimately lie somewhere in between these two extremes, with rates perhaps somewhere in the hundreds per hour. The prescence of the Last Quarter Moon wont help matters any either, but it would certainly be great if we have an opportunity to observe unusually high (ZHR >100) activity on two consecutive nights in 2000. But as November 18 is the "Wild Card" night, all bets are off.

To quote Rob McNaught in a recent e-mail discussion that the two of us had on this subject a short while back: "As with every year, you just have to go out and take your chances!"

-- joe rao

Rainer Arlt

(4 october 2000)

Rob McNaught wrote:

> David and I have never made a bold claim about 2000 and we have never > said that high rates could not occur. Our analysis, that relies heavily > on ZHR estimates from the last 200 years. All we can say is that there > is no historical data that allows us to calibrate our analysis for 2000. > While we suspect rates will be low, we cannot, and do not, discount > the possibility for high rates. The situation for 2001 and 2002 is > rather different. The geometry of encounter is similar to that > experienced during the last 200 years, so we feel more confident in > high rates in these years.

Thanks, Rob, for this additional comment on the predictions. As I just came accross Peter Brown's PhD thesis in my book-shelf, I'd like to add the result of his study here, too:

Brown used large sets of particles ejected at various perihelion passages of the Comet, and followed their motion over up to 2000 years. In the big models, about 1 mill. particles are comprised. This is why he is able to give ZHR predictions based on actual particle numbers being close the Earth's orbit at the right time.

For 2000, he finds the 1733 ejecta (8-revolutions) to be the main contributors. He gives an encouter time at 8h20 UT on November 18 (unlike Rob and David: 3h44). The 1866 ejecta (4-rev) are also involved at roughly 1/4 of the 1733 intensity. For the activity level, he writes: "It is probable that a strong shower, and possibly a small storm, may occur in 2000, but it would likely be smaller than the 1999 shower. Peak ZHRs in this year are more likely in the range of a few hundred..." Now, we should look up what he said for 1999 in order to 'calibrate' the prediction: "We tentatively estimate a peak ZHR of order 1000-2000 with a peak slightly after the nodal longitude of Tempel-Tuttle in 1999."

These sentences give an independent hint on that we will see more than ZHR=20 this year. Now, make up your observing plans!

Best wishes, Rainer

Rob McNaught

(19 october 2000)

Dear all,

David Asher and I have written a piece for the next issue of WGN that summarises our expectations for 2000. We have discussed/critiqued some other approaches to ZHR predictions and made clear the limitations of our method. This note is being sent now to meteorobs for two reasons. Firstly Sky and Telescope 2000 Nov., p 111 makes two statements about our work that are erroneous, and I want to correct these before anyone gives up on the 2000 Leonids. The second is that there are two wonderful coincidences in this year's Leonids that will allow the derivation of valuable data about dust trail structure from visual observations. WE NEED YOUR OBSERVATIONS! (well, via the IMO!)

"... David Asher and Robert McNaught, forsee just a 'normal' display of up to 100 meteors per hour ..." S&T 2000 Nov. p 111 Whilst our nominal predictions is of ~100, we do not discount, and never have discounted, the possibility of storm activity. Our analysis relies heavily on historical ZHR measures *for dust trail encounters*, and none exist for the geometry being encountered in 2000 November (4 and 8-rev trails). I suspect activity will be "low", but could still be the best meteor shower many observers will have seen.

"This year will truly put the Asher-McNaught meteor-trail theory to the test ..." S&T 2000 Nov. p 111 From the comments above, it is clear that we make no strong prediction, so unless substantial activity occurs well away from a dust trail encounter, there will be no test of our theory this year. Only Ferrin, amongst those who have made predictions, has done so without consideration of the existence of dust trails.

I've seen various values for our ZHR predictions floating about. Our latest predictions are those that appeared in Sky and Telescope 2000 June, p 32. The "?" appearing after the predicted ZHRs of 100 for this year are there for a very good reason, as stated above. Hopefully we'll have another look at representing the lower activity extremes of dust trails in the next couple of weeks, but with such limited data available for dust trail encounters, such extrapolations will always be unreliable. However, this year will provide much needed data in this regard, so even if predictions are questionable, the observed ZHRs from dust trail encounters this year *will be extremely valuable*.

The following dust trail encounters are within 0.0050 AU of the Earth

                              distance     ZHR
2000 Nov. 17 07:53 UT  2-rev  -0.0012 AU     ?
             08:22     1-rev  +0.0031        0
          18 03:44     8-rev  +0.0008      100?
             05:51     6-rev  +0.0030        0
             06:44     5-rev  +0.0028        0
             07:51     4-rev  +0.0008      100?

For miss distances of between 0.0000 AU to -0.0007 AU, the time of prediction appears to be accurate to around 5 minutes. This indicates that the dust trails are basically flat sheets, and this is in fact the first observational evidence to that effect (see McNaught and Asher, Meteorit. and Planet. Sci 2000, pp **-**) The timing for more distant trails may be less precise, but as we argued in the above paper, there is no observational evidence for distant dust trail signatures in the 1965 or 1998 observations (nor does the IMO analysis indicate this for 1999). We do not expect any young dust trail encounters to give a broad maximum (FWHM >~1 hour), but this year will be a good opportunity to gather suitable data.

In the above table, only the miss distances are given for several dust trail encounters. Other relevant parameters are the minimum ejection velocities (represented by da0 in our original paper) and the dilution of the trail density with age (fM in our original paper). We feel confident that the 1, 5 and 6-rev trails will produce activity lower than the likely background activity, but 3 trails are worthy of special effort.

Several authors have previously published predictions of detectable activity from the 2-rev trail in 2000. We certainly consider this as a possibility, although believe such activity will be much lower than the 4 and 8-rev trails. If the 2-rev trail is significant in relation to these other two trails, this will indicate a substantial assymetry in the dust trail profile in the sunward/anti-sunward direction and/or a notable aging effect additional to trail stretching (the only aging factor we belive is important). [In the upcoming note in WGN, David and I comment on four errors in the analysis of Jenniskens et al from the June 2000 WGN, as mentioned in the June 2000 S&T p. 32, which had suggested there was an error in our assumed position for the core of the dust trails.]

The two coincidences in this years trail encounters are

1) the 4-rev and 8-rev trails are encountered at the same geometry of +0.0008 AU. This would mean that differences in the observed ZHR are caused by aging factors alone. Or at least they will be if the disruption of the 8-rev trail due to perturbations is not major! Analysis of this may be difficult, but the European longitude observations of the 8-rev trail and the 4-rev from the Americas four hours later will prove interesting.

2) the 2-rev trail and the 4-rev trail encounters occur exactly 1 day apart (well, within 2 minutes sidereal time!). This means that observers using the same location, observing in the same direction and, hopefully, in the same conditions (Moon will make a minor difference) will get directly comparable data on these two trails. Both the relative intensity and the magnitude index will be important results.

So my advice is to get out and observe, not that readers of meteorobs need any such encouragement! Also, if you are not at European or American longitudes your observations are just as valuable. Any outburst must be related to the background activity and who knows, something unusual might happen. Don't forget the occasional Leonid (or Taurid!) fireball and those wonderful long duration trains. Perhaps 2000 won't amount to much, but if such is the case, you should feel well satisfied that your observations will go towards refining the various theories of the structure of the Leonids.

Good luck!

Cheers, Rob

Robert H. McNaught

Reference: R.H. McNaught, D.J. Asher, "Variation of Leonid maximum times with location of observer", Meteorit. Planet. Sci. 34, 1999, pp. 975-978

Joe Rao

(19 october 2000)

In a message dated 10/19/00 3:22:38 AM Eastern Daylight Time, rmn@aaocbn.aao.gov.au writes:

<< "This year will truly put the Asher-McNaught meteor-trail theory to the test ..." S&T 2000 Nov. p 111 From the comments above, it is clear that we make no strong prediction, so unless substantial activity occurs well away from a dust trail encounter, there will be no test of our theory this year. Only Ferrin, amongst those who have made predictions, has done so without consideration of the existence of dust trails. >>

Rob (and everyone else on the meteorobs list) --

That S&T comment about " . . . the Asher-McNaught meteor trail theory truly being put to the test" this year, was that a year 2000 prediction concerning significant Leonid activity based on the meteor trail method was targeting the time frame from roughly 18 to 24 hours after the Earth passing the descending node of 55P/Tempel-Tuttle. Previous to the publication describing the meteor trail method in great detail in journals such as "The Astronomer" and "WGN" I had never seen a prediction calling for any significant Leonid activity so far after the "traditional" time of the nodal crossing. As we are all aware, from a historical standpoint, the Leonids are usually a very sharply peaked display and usually produce just a single "burst" of activity (be it a storm, or a much lower rate).

Last year, many of the "Leonid pundits" called for the possibility of major activity on the morning of November 18. David Asher and Rob McNaught targeted 2:08 UT, but in fairness, there were many others who also were predicting maximum within 10 to 20 minutes of this same time. In one case, Dr. Edward K.L. Upton, of the Griffith Observatory in Los Angeles wrote an article in the popular glossy "Griffith Observer" and made a prediction that the Earth would interact with material shed by Tempel-Tuttle from its 1899 perihelion. He wrote:

"The moment of encounter should be close to 2 a.m., Greenwich time, November 18. This shower will therefore not be seen in America, but all of Europe and all of Africa except the easternmost tip will be favorably positioned. A due regard for the height of the radiant and likely weather conditions points to North Africa as the best observing location."

As we all now know, the 1999 Leonids reached their peak near 2:02 UT. The interesting point about Dr. Upton's article is that it appeared back in May 1977. Upton's entire article (including an introduction by Dr. Ed Krupp and myself) is reprinted in the current Griffith Observer (November, 2000/Vol. 64, No. 11).

Concerning the Leonids in 2000, most of the predictors have targeted the morning of November 17 (again around the node) as the most likely time for highest activity. Rob and David's prediction for potential maximum activity occurring on the morning of November 18 pretty much has stood alone (although Esko Lyytinen and Tom Van Flandern have now also cited the morning of the 18th for maximum activity, though taking a somewhat different approach than Rob and David).

The point that S&T tries to make is that if any surge of Leonid activity is observed on the morning of the 18th, that it should certainly should go some ways to help validate the meteor trail theory. In a personal e-mail to both David and Rob, I commented that the meteor observing community owes both of them a debt of gratitude for being the first to step forward and point out the possibility of some unusual activity occurring on the morning of the 18th. Only a few years ago, the vast majority of observers would have concentrated all of their efforts on the morning of the 17th . . . and most would likely have not bothered to look again on the following morning! As I pointed out in a message here a few weeks ago, this upcoming scenario of possible distinct/significant Leonid activity on two consecutive nights is rather unique in the modern history of the Leonids . . . and perhaps will only serve as a precursor to Rob and David's projection of multiple storm peaks in 2001!

Concerning Dr. Ferrin's prediction of a major Leonid storm this year on the morning of the 17th, I should point out that it very much mirrors a similar prediction that he made concerning a possible storm of Giacobinid meteors for 1986. In a letter to Sky & Telescope, published early that year (February or March . . . I don't have it at hand), Dr. Ferrin suggested even greater Giacobinid activity a year after the 500/hr rates observed from Japan in 1985. He does not specifically mention his "isolines" method in his letter, but his reasons and conclusions for expecting a major Giacobinid display in 1986 seems to closely parallel his projection for major Leonid activity a year after last year's storm-level event. As for the 1986 Giacobinids, little or no activity was noted.

Echoing Rob's sentiments, I say regarding the Y2K Leonids: you'll only know what will really happened if you get out and look!

-- joe rao

Rob McNaught

(20 october 2000)

Okay, Joe, understood, but I rather thought there should be no doubt about the reality of dust trails. However, I guess that is not for me to judge. The only question in my mind was in the calculation of the rates. If you refer to Fig 9, of our original article, you will see that the year 2000 is the first year in the last 200 years that two substantial outbursts are possible in the same year (use ZHR0). There is thus no reason to be surprised by the lack of any precedent.

Having read Upton in the last several months, it is apparent that he had a clear understanding of the dynamics involved and appears to have been the first to come up with dust trail calculations for the Leonids. Dust trail calculations for the Draconids predate Upton however. All the dust trail calculations I've seen by different authors have agreed within minutes. Methods using averaging of many test particles sometimes differ due to the binning over time and space being too coarse. The direct dust trail calculation overcomes this by making a few iterations of a single particle.

Perhaps it appears arrogant to some, but it was clear to David and I that the dramatic correspondence of the time of maximum (within about 5 minutes) from dust trail calculations for the Leonids in 1866, 1867, 1869, 1966 and 1969 and that independently determined by Peter Brown from historical observations of these Leonid storms and short duration outbursts, was not due to chance. There were no discrepant timings. In our view, questioning this was questioning Newton, and the situation was never in doubt in our mind. The time of maximum in 1999 came as no surprise to us. Just what is required? If nothing much happens this year, will such uncertainty remain for another year? I had assumed the test being suggested was of the dust trail density model which is independent of the, in our view, well confirmed dust trail theory. The dust trail theory has been independently "discovered" numerous times simply because it is relatively straight forward to conceptualise and requires, in its most basic form, only Newtonian dynamics.

Cheers, Rob

Robert H. McNaught

Peter Jenniskens

(19 october 2000)

Information on the observing conditions for this year's Leonids are given at: http://leonid.arc.nasa.gov/estimator.html

This program allows you to calculate the expected apparent Leonid shower rate for any given location and a range of observing conditions (city, suburb, country side, mountain top).

The program includes my estimates for peak rates of ZHR = 210 for passing the 1932 trailet and ZHR = 70 for passing the 1866 trailet the next night. Those estimates compare to ZHR = 215 and ZHR = 700 respectively by Esko Lyytinen and ZHR about 100 by Robert McNaught and David Asher.

The peak times are based on McNaught and Asher and Lyytinen's calculations. The width of the shower was calculated based on our find that the dust trail cross sections tend to be Lorentzian in shape, assuming that they are Lorentzian as well perpendicular to the dust trail. We'll soon find out.

I've also included a Leonid Filament component, based on high rates in 1967.

Remember: the Nov. 16/17 encounter with the 1932 dust trail is unique and the encounter with the 1866 dust trail the next night is a preview of what to expect in years to come. Don't be discouraged by the bad Moon. Shielding it behind a pole or some other thin and high object will go a long way giving you a nice view on the sky.

Peter Jenniskens

SETI Institute
NASA Ames Research Center


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