Leonids 1997: prospects

Marco Langbroek, Peter Jenniskens, SKY Online's Meteor Page, Joe Rao, Peter Bus

We are now only one year distant of the great storm. Last years 1994 to 1996, the stream already showed clear enhanced activity. For 1997, prospects for high rates are good but the moon will severely hamper. Nevertheless, the stream can provide some spectacular moments.
Predictions are very difficult, so please note that this is only an expectation and reality might show to be different. Yet, most likely is that the stream will peak on November 17 near 12-14h UT, favourable for the Pacific, with peak rates that might be near ZHR ~200. If the outburst component is as broad as during previous years, European observers might experience rates near ZHR ~80 on the night of November 16/17 and rates near ZHR ~60 on the night of November 17/18.
In addition to this broad component, observers in the west of the USA might be presented with a very steep narrow activity component superimposed on the broad background, consisting of faint meteors, somewhere near 10-12h UT. During this period, activity can become very high though presumably not yet at a true storm level. This narrow peak of less than 2 hours duration is due to the future storm component. It was observed last year by Dutch observers observing from France.
Observers should take great effort not to neglect faint meteors. The moon will be a problem in this aspect, but it is also clear from last year's reports that many observers neglected the faint meteors because they were too much pre-occupied with the many bright fireballs that appeared.

- Marco Langbroek
Dutch Meteor Society

Be sure to visit the "Leonids 98: Meteor Outburst Mission Homepage" maintained by Dr. Peter Jenniskens of NASA-AMES. You will find evenything you were searching for on the Leonids!

Some links regarding the Leonids adapted from SKY Online's Meteor Page:

Leonids 1997: prospects

The message below was sent by Joe Rao to meteorobs. The information, however, is of interest for all observers, so we repeat it here. I just changed the times to UT.

On Monday morning, November 17th, the Leonid meteors are scheduled to reach maximum. This year is particularly interesting, in that the parent comet of this particular meteor swarm -- 55P/Tempel-Tuttle -- is due to arrive at its perihelion on February 28th of next year. Because of these circumstances, there has been some discussion about the possibility that a meteor storm "could" occur. In some ways, the upcoming Leonid shower does indeed bear a similarity to the comet-Earth geometry that accompanied the Great Leonid Meteor Storm of 1799, which was observed from Peru by the Prussian scientist and explorer, Alexander von Humboldt.

In that particular case, the Earth led the comet to the descending node by 116.9 days. Similarly, this year, the comet follows Earth to the node by 108 days.

However... the respective orbits are much farther apart in 1997 as opposed to 1799... the difference being 0.0048 a.u. or approximately 718,000 kilometers. Thus, the odds of a storm are greatly reduced.

Nonetheless, it will certainly be worthwhile to keep a careful watch for any potentially unusual meteor activity; with the parent comet so close to its nodal crossing point, there is always the possibility of a brief outburst of activity... and/or some unusually brilliant fireballs or bolides. Last year, reports received indicated meteors that left luminous trains for in excess of five minutes. One especially brilliant meteor seen over the Canary Islands, left a trail that lingered for nearly 30 minutes!

There are two specific time frames to be especially alert to. One is when the Earth crosses the comet's node, which is to occur at 13:34 UT on Monday.

The other time frame is 10:40 UT. This corresponds to the moment when the Earth will be passing that part of 55P/Tempel-Tuttle's orbit which produced the epic meteor storm of 1966. According to Mr. Peter Brown of the International Meteor Organization (IMO) some slight enhanced activity has been noted near this region of space during the last two Leonid showers. It will be interesting to see if anything unusual is again noted this year when the Earth once again encounters this region of space.

The major drawback of this year's Leonids will be the bright light of the 89% waning gibbous Moon, which will positioned near Orion's upraised club -- roughly 55 degrees west of the Leonid radiant. No doubt a large number of faint meteors will be washed-out by the Moonlight, but with the hope of sighting some bright fireballs and bolides, it may still be worthwhile to get out and observe. Some may use the Moon as an excuse not to get out and observe, but this year's Leonids may be worth the effort.

Meteors appear to fan-out from the "Sickle" of Leo. The Sickle rises out of the east-northeast around midnight and is high toward the south-southeast by dawn. If you do go out and observe, we'd sure like to hear about what you've seen. Good Luck!

Joe Rao

Obervations under moonlit conditions are normally not recommended. However, a reliable information about the time and (approximate) strength of the Leonid maximum a year ahead of a major peak is of great interest. In order to reduce the bad influence of the Moon, arrange your place in such a way that it is somewhere behind a building or something else. This is difficult as long as the Moon is high in the sky, but easier towards the morning. Reports should be split in 15...20 minute intervals.

Clear skies and Good Luck!

Jurgen Rendtel
IMO President

Leonids 1997: prospects

Additions to Joe Rao's message.

At the time The Great Leonid Meteor Storm of 1799 occurred, the Earth led the comet to the descending node at about 117 days. After Joe Rao the odds of a storm are greatly reduced because the orbit of the comet is in 1997 on a greater distance from the Earth than in 1799. However, there are more storms reported in the past when the Earth led the comet to the descending node on less than 150 days. These storms occurred in 1366, 1532, 1566, 1799 and 1832. In all cases the distance the orbit of the comet was smaller than in 1997. In 1532 the distance was about 0.0064 AE between the orbits ( in 1997 about 0.0079 AE) and the Earth led the comet at 135 days. In many sources, it can be read that in 1865, when the Earth led the comet at 65 days, the Leonids produce no storm. However, nodal passage took place on 1865 November 13 at 17h UT and a possible storm was only visible above the Western Pacific. Note that absence of records not necessarily means that a storm was absent.

My radio observations of the Leonids of 1996 show clearly two peaks. The first one at Solar Longitude 235.16 (Equinox 2000.0). This position is the same as observed for the outburst in 1966. The second peak, higher than the first (in spite of unfavorable antenna geometry), was observed at Solar Longitude 235.27. This position coincides with the predicted time that the Earth passes through the orbitplane of comet 55P/Tempel-Tuttle in 1996 computed by Yeomans, Yau and Weissman.

It does seem likely that this was the first appearance of the "nodal" peak of the Leonids in this Leonid season.

Eisse Pieter (Peter) Bus

Leonids 1996: revised data

Hello everybody,

Recently, I have taken a new look at our 1996 Leonid data from the 'narrow peak' period. I recalculated rates from our data with more up to date values for perception etc. This puts Koen and my observations more on line (my Cp has changed to 1.4: I calculated with 1.2 in my initial WGN report).

The difference is not big. Rates come out slightly lower when pouled. Still compatible with a B~30 peak with ZHR ~90-100 on a background ZHR of ~50, combined resulting in peak ZHR ~140-150.

That is still higher than in the last ILW bulletin (#10, see last WGN issue) , and that difference is too large to be solely due to a different choice of some parameters (actually, only gamma and the inclusion of perception correction is different in our analysis) Reasons could include:

  1. Our rates are slightly too high, because some of us might have a slightly better perception for faint meteors than average.
  2. The ILW rates are to low because of: larger intervals, use of sliding mean, but most notably, I suspect it includes observers who did not pay full attention to the faint meteors, lowering their ZHR. This could explain the scatter that is noted in the ILW analysis. Note that in the ILW bulletin this effect is remarked upon (the missing of faint meteors) in the context of the r-values determined.

I suggest both explanations might be at play. Given the uncertainties in both analysis, I think it is best to conclude that the 1996 narrow peak maximum ZHR was somewhere between 100 and 150.

-Marco Langbroek
Dutch Meteor Society

Revised rates.
Data before 3:40: M. de Lignie and J. Nijland.
After 3:30: M. Langbroek and K. Miskotte.
See also report in WGN December 1996.

LEONIDS 16/17 NOV 1996

    UT ZHR +/- 3:08 57 10 3:37 62 13 3:55 76 15 4:10 83 12 4:29 87 12 4:49 143 17 - clouds- 5:47 73 18

Note: r=2.5 was taken, but since Lm was ~ +6.5, this has little to no influence on the rates calculated.

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