Photographic observations by Hans Betlem from (California, USA)
Video-observations by Hans Betlem (California, USA)
Visual observations by team Delphinus
More preliminary ZHR results (Europe too)
Radio observations by Peter Bus, Groningen
Visual observations by Carl Johannink at VST-Lattrop
Visual observations by Alex Scholten at VS-Bussloo
Leonids in the Moonlight : Sky @ Telescope News Bulletin
LEONID METEORS 1997 : IAUC 6772 of the IAU: CBAT
Preliminary ZHR California november 17
LEONIDS 1997 : IMO Shower Circular (Rainer Arlt)Dear Everybody,
We have tried a campaign on the night of 16/17, both visual and multistation photographic, in the Dutch/German border area. Though not the entire night, we have been able to observe. Below our impressions.
Team 1 (Koen Miskotte, Carl Johannink and Jos Nijland) was at Lattrop public observatory in the easternmost part of the Netherlands and could observe for two hours from about 0:15 to 2:30 UT
Team 2 (Robert Haas and me (=Marco Langbroek)) made a 'grand tour' through norteast Netherlands and parts of Germany, tried to find a location without haze and stratus. We found it near Meppen, only just over the Dutch/German border (but it later turned out that it had been better if we had gone some 30-50 km more to the east). We observed from 1:45 to 2:45 UT. Then, a cirrus front coming from the west that also hit Lattrop culled us off.
Both stations had Lm near ~ 5.4-5.7. Rates were clearly enhanced, but not as much as we had hoped for. We don't have our data available yet, but our impression is, trying to account a little bit for the moonlight, that rates were similar to the 1995 return, i.e. ZHR around 30-40 or so. What struck us was that in comparison with both 1995 and 1996 there weren't that much real bright meteors. The Lattrop team however has seen one -6, with 3 minutes persisting train. I saw a -2 as my brightest during my session, and a -4 tru cirrus in twilight when back at Lattrop. To be clear: the meteors were certainly brighter than the normal annual display, but not to the extend as in 1995 and 1996.
So, a little bit ambiguous. We are glad to have been able to do some observing, especially given that last days in the forecast it didn't look like we would be able to do so. And yes, there was a fine enhancement. But from the perspective of rates and brightness, it could have been better.
That's it for the moment. We are now back again at Casper's place to look at the forecasts for coming night and the last satellite pictures. Probably, we will be active from the eastern part of our country again, which when we left had good clear skies (the cirrus had dissolved). Problem is that the electricity generator of team 1 has broke down, so we have to position them somewhere where they have an electric socket available (such as at a public observatory).
-Marco Langbroek
Dutch Meteor Society, the Netherlands
Also on behalf of:
Koen Miskotte
Jos Nijland
Robert Haas
Hello everybody,
This is a weird campaign. Last night (early in the evening) it looked like we would have to go to the east of our country again. We had already left, when we received word that there could possibly be cloud interference coming from |Germany in the east later that night, but.....that the center of our country was clearing! One of our 2 teams already had reached the publ;ic observotory at Lattrop in the east of the Netherlands, but Robert and I were just 30 km east of our regular location Biddinghuizen and decided to turn and go to that location.
When we arrived, the sky was as clear as crystal. Much to my amazement, I counted an Lm of 6.0, which is perhaps the best I have ever experienced for moonlight conditions! We could even see some marginal milky way from Cassiopeia to Cygnus! So we decided to stay and setup. After setting up our photographic equipment, we took a short sleep, and started observations fresh (...) at around 0:45 local time (23:45 UT).
In the early part of observations, the Leonids were showing a clear activity, though evidently less than the previous night. Several attractive bright meteors up to -3 appeared. But later that night, rates were evidently and seriously in decline: we really experienced (so to speak) that they did fall off markedly, the stream just petterred out so to speak. It was brilliantly clear, but also frosty (temperatures slightly below freezing) and the eastern wind was strong and very cold. The last hours were really unpleasant because of the cold wind and the actually quite unaspiring activity around that time.... Meteors now seemed less bright too.... But our perseverance was rewarded with a beautifull brilliant blue -6 Leonid at 5:12:16 UT that had 2 minutes of persisting train, drifting gently away....
This night, we also saw some nice Taurids including a loooooooooong -2.
Tomorrow or the day after, I will mail my data of last two nights. Like I wrote before, definitely enhanced activity, a nice show (particularly 16/17 and early in the night 17/18, but less than we had hoped for and in that aspect slightly disappointing. But it was a good campaign.
Last night we certainly obtained some multistation photographic orbits of Leonids.
-Marco Langbroek
Dutch Meteor Society, the Netherlands
Hello,
Below the data of Koen Miskotte and me (=Marco Langbroek) of 16/17 and 17/18 november.
(Rainer: I will not send this set tru postal mail, so this is my only submission -ML)
Obs: Koen Miskotte - MISKO
Loc.: Lattrop P.O., 52d 26' N, 6d 58' E (The Netherlands)
date: 16/17 nov 1997
UT Teff Lm Leo Tau Spo
0:22-1:15 0.88 5.4 6 0 3
1:15-2:15 0.98 5.2 7 2 5
Stopped because of upcoming clouds. Moonlight, but clear.
-5 / 0 1 2 3 4 5
Leo 1 1 3 2 4 2 0
Spo 0 0 0 1 3 4 0
Tau 0 0 1 0 1 0 0
Date: 17/18 Nov 1997
Loc.: see above
UT Teff. Lm Leo Tau Spo
23:02-0:15 1.22 5.7 9 3 14
0:31-1:30 0.98 5.5 10 1 15
1:30-2:30 1.00 5.45 6 0 11
2:48-4:10 1.37 5.3 9 1 6
-2 -1 0 1 2 3 4 5
Leo 1 2 5 6 4 13 3 0
Spo 0 0 0 0 10 22 14 0
Tau 0 1 0 1 1 1 1 0
--------------------------------------------------------
Obs.: Marco Langbroek - LANMA
Location: Ruelingermoor, 52d 41'N, 7d 55'E, GERMANY
date: 16/17 Nov 1997
UT Teff Lm Leo Tau aMo Spo
1:48-2:42 0.90 5.7 24 2 2 7
Stopped because of upcoming clouds. Moonlight, but clear.
-2 -1 0 1 2 3 4 5
Leo 1 1 1 0 6 9 6 0
Spo 0 0 0 1 1 2 3 0
Tau 1 0 0 0 0 1 0 0
aMo 0 0 0 0 1 1 0 0
loc.: Biddinghuizen, 52d 29'N, 5d 41' E, The Netherlands
date: 17/18 Nov 1997
UT Teff Lm Leo Tau aMo Spo
23:45-1:05 0.97 6.0 18 1 0 9
1:05-2:05 1.00 6.0 16 2 2 6
2:05-3:00 0.92 5.9 18 2 0 9
3:00-4:15 1.05 5.9 17 2 1 14
4:15-5:37 1.30 5.6 24 1 1 10
-6 / -3 -2 -1 0 1 2 3 4 5
Leo 1 2 2 3 2 7 15 42 17 2
Spo 0 0 0 0 0 0 13 25 10 0
Tau 0 0 1 0 1 0 2 3 1 0
aMo 0 0 0 0 0 0 2 2 0 0
Moonlight, but extremely clear. Even part milky way marginally visible!
Note: Both Koen and I suggest to be somewhat cautious in regard to the meteor magnitude estimates. Perhaps, we slightly estimated to faint because of the moonlight.
-Marco Langbroek
Hello again,
Below some VERY preliminary ZHR-results from our Dutch observations, to add to the preliminary ZHR for california I communicated earlier. Again: please regard this as an indication of rate level only. It is based on data from 3 observers: Carl Johannink, Koen Miskotte and me (=Marco Langbroek).
In general, ZHR's were around ~50 for early november 17 as observed from Northwest Europe. Unfortunately, our observing interval was short due to clouds. The next night, 17/18, saw a ZHR that decreased clearly over the night, from about ~40 to ~30. Coupled to the ZHR ~115 seen from California (note: based on Bob's data only, so be carefull!), this agrees excellently with a B~1 component peaking at around ZHR ~115 (annual + outburst combined: outburst only ~100) above the western USA, with B describing rate behaviour as in the next equation:
ZHR = ZHR_max * 10^-B|l-l_max| (See Astron. Astroph. 295 (1995), 206)
...with l= solar longitude
This means that a similar broad B ~1 (and bright) component as in 1994-1995-1996 has been present, this time with a peak ZHR near 100.
It is not clear whether a narrow peak was also present, as in 1996. Perhaps Bob and some others saw the onset after 13:00 and the narrow peak then might have peaked just after the end of the Californian time window, over the western Pacific perhaps. But as George noted, 'storm'-rates have not been seen by Californians themselves, judging from the reports and Bob's data.
Below some ZHR's for the European intervals, as described above, calculated for r=2.0 with gamma=1.4 and perception taken into account (Carl: 1.0: Koen: 1.2; Marco: 1.4).
Nov 17 UT ZHR +- 1:30 50 8 Nov 18 UT ZHR +- 1:45 42 5 3:42 28 4
Add these to the values from Bob's observations from west USA send earlier (ZHR's around 115, except for last hour which might have been higher). The outburst was present for about one day, with Europe seeing rates going up the one night and down the other, and the USA having the privilege of the peak.
-Marco Langbroek
Dutch Meteor Society
Forward-scatter observations of "sporadic" meteors in November 1997 Observer : Eisse Pieter (Peter) Bus Location : Groningen, Netherlands (6 degree 33' E, 53 degree 13' N) Frequency : 72.11 MHz Transmitter Location : Wroclaw, Poland, 130 kW, Distance 740 km Antenna : Yagi, 3 elements, geographical azimuth 106 degrees (ESE), elevation 13 degrees. Receiver : Bearcat UBC 860 XLT Scanning radio, sensitivity 0.5 uV. Observation Method : Listening and counting in 5-minute intervals. Mean "sporadic" activity of long-duration reflections > 7 sec on 1997, November 2,8,9,12 and 14 starting at UTC: 4h 5h 6h 7h 8h 9h 10h 11h 12h 13h 3 3 2 2 2 2 2 2 1 1 No long-duration reflections monitored > 20 sec ! On November 9, 12 and 14 only a part of the observation period is monitored. November 9, 8 - 14h UTC; November 12, 4 - 6h UTC and on November 14, 6 - 14h UTC. The results of "sporadic" activity for 1997 is almost the same as monitored in 1995.
Results of 1997 November 15 Forward-scatter observations of long-duration reflections > 7 seconds starting at UTC: 6h 7h 8h 9h 10h 2 2(1) 3(1) 3(1) 2(1) Between brackets the number of long-duration reflections > 20 seconds.
Results of 1997 November 16 Forward-scatter observations of long-duration reflections > 7 seconds starting at UTC: 6h 7h 8h 9h 10h 3(0) 7(3) 5(2) 4(0) 3(0) Between brackets the number of long-duration reflections > 20 seconds. most favourable antenna-geometrie for detecting Leonids between 5h45m and 7h30m UTC.
Results of 1997 November 17
My Radio-observations of the Leonids started in 1993. Since the new season
of the Leonids started in 1994 this is the most active one that I have observed
by forward-scattering of VHF radio waves.
Forward-scatter observations of long-duration reflections > 7 seconds
(oncorrected counts) starting at UT:
5h 6h 7h 8h 9h 10h 11h 12h 13h
21 19 22 22 13 20 16 4 4
(14) (12) (10) (18) (5) (8) (6) (1) (1)
Between brackets the number of long-duration reflections > 20 seconds.
Between about 8 and 9h UT many long-duration reflection > 100 seconds.
Possible first maximum between 10h and 11h30m UT (Solar Longitude: 235.17)
Because Radiant below horizon no data around nodal passage.
In 1996 a Radiomaximum is observed at Solar Longitude 235.16 and 235.27)
Notes: For the mid-point of the transmitter-receiver path:
Radiant rising on November 16 at about 21h30m UT.
Radiant setting on November 17 at about 13h40m UT.
Most favourable antenna-geometry for detecting Leonids:
between 5h45m and 7h30m UT.
Unfavourable antenne-geometry after 10h UT.
Very unfavourable antenne-geometry after 12h UT.
Radio Hour Rates of the Leonids of 1997 November 17
Very preliminary results!
After correction of 'dead-time", "sporadics" and Observability Function after
Hines, the very preliminary results of my radio-observations are given.
| For this period the results are NOT reliable
| because the very unfavourable antenna-geometrie
___________________________________________________________________________________
|
5-6 6-7 7-8 8-9 9-10 10-11 | 11-12 12-13 13-14 (Time in UT)
29 22 26 29 20 64 | 43 30 30 (Hour rates)
(6) (5) (5) (6) (6) (14) | (13) (20) (20) (one-sigma errors)
Probably a first maximum is observed between 10h and 11h30m UT,
nearby Solar Longitude 235.17 degrees (Equinox 2000.0). Almost on the same position
as observed in 1996. A "nodal" peak is not monitored because for the mid-point of
the transmitter-receiver path the radiant was on that time below the horizon.
Results of 1997 November 18 Forward-scatter observations (uncorrected counts) of long-duration reflections 7 seconds starting at UTC: 6h 7h 8h 9h 10h 11 11 10 7 5 (10) (10) (1) (3) (1) Between brackets the number of long-duration reflections > 20 seconds.
Preliminary Results of Radio Meteor Scatter observations of the Leonids 1997
Since my radio observations of the Leonids started in 1993, and the observations show evidently that the new season of the Leonids started in 1994, the Leonids of 1997 were the finest of all because the very long period of high activity on November 17 with many long-duration reflections often over more than >100 seconds.
The first clear Leonid is observed on November 15. However, the total activity on this day was very low.
Radio Hour Rates (RHR) of about <2.
On November 16 the activity of the Leonids was slightly increased and a mean RHR of about 6 is found between 6h and 11h UT. On November 17, the higher activity started probably after 0h UT, because until this time no unusual activity is monitored above the "sporadic" activity. When I started my observations again at 4h50m UT the Leonids were already very active. Until 12h UT, high rates are monitored. The mean RHR in this whole period is about 40. After 12h UT the antenna-geometry was very unfavourable and therefore the Radio Hour Rates are unreliable. Probably a peak is observed around 11h UT at Solar Longitude 235.17 degrees (Equinox 2000.0). Almost on the same place as observed in 1996 at 235.16 degrees. At the moment the Earth passes through the orbit plane of comet 55P/Tempel-Tuttle the radiant of the Leonids was just below the horizon. Therefore a peak is not monitored as observed in 1996 around Solar Longitude 235.27 degrees. Because activity was still monitored after 12h UT, perhaps rates were higher in the last hour. On November 18 the activity was still high with a very constant RHR of about 10.
Below all the Radio Hour Rates are given. All are corrected for dead-time (*), sporadics and observability function after Hines[1].
Time Nov 15 Nov 16 Nov 17 Nov 18 in UT 5 37 (7) 6 0 (2) 2 (2) 26 (5) 12 (4) 7 0 (2) 9 (3) 29 (6) 14 (4) 8 3 (3) 5 (3) 40 (7) 10 (4) 9 3 (3) 5 (4) 23 (7) 10 (5) 10 0 (4) 6 (6) 73 (15) 9 (7) 11 53 (14) 12 40 (22) 13 40 (20)
Between brackets one-sigma errors with the errors of sporadic activity taken into account.
Please note on 72 MHz, I can only receive Leonids of about visual magnitude +2 or brighter!
(*) Dead-time marks the period in which a certain signal of amplitude may mask other signals of lesser amplitude.
The dead-time were applied according to the "Geiger-counter method".
[1] Hines, C.O., Can. Journ. Phys. 22, pp. 493-503, 1955
VISUAL RESULTS LEONIDS 1997
Clear skies in november are very rare in the Netherlands, especially during the Leonids. But 1997 is an exeption! The night 16/17 was partly clear and 17/18 completely. Unfortunately I had to go to work both days. Beiing a teacher isn't always the ideal job... So I observed these nights only for some hours. Below are the results. Observing with Rita Verhoef, Arnold Tukkers, Ralf Mulder, Patrick Schiphorst from our Observatory, and Koen Miskotte and Jos Nijland from 'Biddinghuizen' was very pleasent.
Carl Johannink
=======================================================
*Date : 16/17-11-97
*Observer: Johannink, Carl (IMO-code: JOHCA)
*Place : Lattrop (Netherlands)
*Coord. : 6o 58'E ; 52o26'N
*Center : R.A.=02h; Decl.=75 deg. at 00:30 UT
*Start : 00:10 UT
*End : 02:15 UT
*Teff : 2.08 hours
Time(UT): L: T: spo: N: LM: notes:
00:10-01:15 6 1 3 10 5.0 1.08 hours
01:15-02:15 6 1 3 10 5.0 (*)
(*)= after 01:45 UT clouds appeared in the western sky.
At 02:15 UT my field of view was obstructed for 40% .
End of session.
=======================================================
*Date : 17/18-11-97
*Observer: Johannink, Carl (IMO-code: JOHCA)
*Place : Lattrop (Netherlands)
*Coord. : 6o 58'E ; 52o26'N
*Center : R.A.=02h; Decl.=75 deg. at 00:30 UT
*Start : 23:25 UT
*End : 02:25 UT
*Teff : 3.00 hours
Time(UT): L: T: spo: N: LM: notes:
23:25-00:30 9 1 5 15 5.4 1.08 hours
00:30-01:30 9 - 6 15 5.4
01:30-02:25 8 - 4 12 5.4 0.92 hours
-------------------------------------------------------
C.F. Johannink
Schiefestrasse 36
48599 Gronau
Germany
phone : + 49 2562 22345
email : cjohannink@compuserve.com
-------------------------------------------------------
The primilary results of the Leonid-campaign November 17/18th 1997 from the Public Observatory Bussloo (Netherlands)
Location: Bussloo (NL), 06E 52N
Observer: Alex Scholten (Eerbeek)
Obs.time: 22h06m UT - 05h45m UT
Eff.time: 6.8 h
Lim.magn: 5.5 (moon -85% , at 3h30m UT high above southern sky)
Temp. : approx. -1 C
Observed meteors: 45
Leonids: N=30 (47% trails) Non-Leonids N=15 (27% trails)
-5 1 (05.12.14 UT) 0
-3 1 (03.31.15 UT) 0
-2 0 1
-1 1 2
0 2 1
1 5 4
2 10 3
3 7 2
4 3 2
mean magn. 1.63 1.33
UT T-eff Leonids non-Leonids
22.06 - 23.00 0.9 2 4
23.00 - 00.00 1.0 1 2
00.00 - 01.00 0.7 4 0
01.00 - 02.00 1.0 2 3
02.00 - 03.00 1.0 1 2
03.00 - 04.00 0.6 7 2
04.00 - 05.00 0.8 8 2
05.00 - 05.45 0.8 5 0
Note: between 01.35 UT and 02.45 UT no meteors
observed (!!) which resulted in a
decreasing concentration
-------------------------------------------------
A.Scholten@DCS.cnt.antenna.NL
Alex Scholten
Horsterdijk 6a
6961 KP Eerbeek
The Netherlands
phone: (0)313-652716
fax: (0)55-5792214
 |
 |
The 1997 Leonids showed a major event over the western part of the USA. Between 4:00 and 4:30 local time (12.00 - 12.30 UT), tens of fireballs were seen by observers in Southern California. There was a period in which about one fireball of -4 or better was seen every minute. Several of them -10 or so. Many long enduring persistant trains were reported. Due to the bright moonlight, no faint meteors were seen.
A three station photographic network was set up by the members of the Californian Bay Meteor Society in cooperation with the Dutch Meteor Society which set up the third station at Edwards Air Force Base. Despite the bright moonlight and the moon nearly in its zenith, it was possible to make good photographs because of the very transparent sky we had at maximum night and the night before. We expect at least 40-50 bright Leonids and fireballs to have been photographed, many of them multi-station photographs. The California stations were set up at Walker Pass (where a small earthquake was also felt!) and at Goldstone test site.
The Dutch station at Edwards Air Force Base was set up in close cooperation with a Canadian radar and video project set up by the NRC (Peter Brown).
More results on this site soon!
Hans Betlem (Betlem@STRW.LEIDENUNIV.NL) and Mike Koop (KOOPM@BEST.COM)
|
-10m Leonid fireball. November 17, 1997 12h11m55s UT. Appeared less than 20 degrees from the moon
and nevertheless produces a bright flash and shadows. A long enduring tran was seen during ten minutes
in broad moonlight. Edwards AFB. Camera : Canon FD f/1.8-50 mm. Rotating shutter at 50 breaks/second. |
| -3m Leonid. November 17, 1997. 12h00m33s UT. Stars of Hya are visible. Edwards AFB. Camera : Canon FD f/1.8-50 mm. Rotating shutter at 50 breaks/second. |
|
 |
-3m Leonid. November 17, 1997. 11h54m46s UT. Stars of LMi are visible. Edwards AFB. Camera : Canon FD f/1.8-50 mm. Rotating shutter at 50 breaks/second. |
| Goldstone Leonid team. November 15/16/17, 1997 at the observing site. |  |
 |
November 16, 1997. Goldstone team changes films in the hotel room. From left to right : Mike Koop, Sandra Mesica and Bob Lunsford. |
Please note: you will need a MJPEG-AVI driver to play these movie-files on your computer! Your computer will probably not have such a driver installed, as it is not part of the Windows'95 installation. A good driver is the one form PARADIGM. Download will start immediately when you click on the link. Installation instructions are on the PARADIGM-website.
LEONIDS IN THE MOONLIGHT (SKY & TELESCOPE'S NEWS BULLETIN)
While no one reported seeing anything close to the historically known "meteor storms" from Last Monday night's Leonid meteor shower, many observers were nevertheless impressed by many bright fireballs. According to S&T contributor Stephen O'Meara, who was observing from the slope of Hawaii's Mauna Loa, there were several instances when the fireballs came in clusters of four or five. The brightest meteor, he reports, was magnitude -4 (as bright as Venus), and exploded with a brilliant white flash and left a train that lasted more than 5 minutes despite the moonlight. His maximum rate was between 13 and 14 hours Universal Time when he observed 41 meteors. The meteor trains varied in color from orange to green. Because the Leonid shower's parent comet 55P/Tempel-Tuttle is due to reach perihelion in February, meteor observers were hopeful that the display would be extra intense. However, it is more likely that the "storm" may come in 1998 and/or 1999.
IAUC 6772 (1997 Nov. 18) : LEONID METEORS 1997
Hello everybody,
I have done some very (VERY) preliminary calculations, using Bob Lunsfords data, to get some insight into the Zenit Hourly Rates (ZHR) experienced for the maximum period, which California presumably experienced or was very close at. You find them below.
Please note that this is very preliminary, and based on one observer only. So, it is only an indication (emphasis) of the ZHR levels. I choose Bob's data for several reasons: he reports a good Lm, made a good set of data available, and from earlier work with his data I now he has a perception which is quite the 'average' or 'standard' perception (i.e. Cp ~1.0). His sporadic rates combined with reported Lm's hint that his perception did not seriously alter due to the moonlight conditions. So for an indication, I think his data will suffice.
I calculated ZHR's in ~1 hour intervals, with gamma 1.4 in radiant altitude dilution (gamma 1.0 would result in only slightly lower rates). I give two ZHR's: one under the assumption of a population index r=2.0, and one for r=2.5. The first assumes emphasis on bright meteors, the second assumes a faint component similar as what we saw in 1996 (but almost unnoticable due to the moonlight). For the moment, I think the r=2.0 column is most appropriate. In the last column, I give Bob's limiting magnitudes for reverence, because variations in Lm of course might influence rates slightly.
r=2.0 r=2.5
UT ZHR +- ZHR +- Lm
10:00 118 24 149 30 5.45
11:00 112 20 144 26 5.35
12:00 114 16 134 19 5.65
13:00 141 19 182 24 5.34
Please note the moonlight circumstances, so take it as an indication only.
Activity seems rather constant at just above ZHR 100. Perhaps, rates where higher in the last hour, but this is sensitive to the Lm estimate (the effect disappears largely if the true Lm was higher). But the report of increased fireball occurence during this last hour suggest that rates might really have been higher (perhaps peaking after twilight set in?). During our 1996 European narrow peak we also experienced a fireball flurry besides the faint meteors (both Koen and me personally saw at leat 12 Leonids of -3 and brighter in one hour).
I did not look at our Dutch results yet (still have to listen to my tapes: due to some personal circumstances that was not possible untill now. Koen will report his data within 1-2 hours from now to me), but if our estimate of ZHR 30-40 during our European Nov 17 night interval is correct, this would pretty well line up with the rates at about 100 or slightly higer for California. It suggest a B~1 structure, like 1994-1996, peaking over west USA/east Pacific.
-Marco Langbroek
Dutch Meteor Society
The 1997 Leonid peak was expected to occur over North American west coast longitudes and Hawaii on November 17. The strong moonlight caused difficulties in determining the limiting magnitudes, resulting in large scatters of the ZHRs. This Circular does not claim to give first average ZHRs -- it rather tries to find the actual peak time. ZHRs should be treated as relative values, since more elaborate calibration of the moonlight observations may be necessary when more data have been received.
The peak time fell between 10h30 UT and 13h UT. The exact time is hard to derive, since several observers reported sharp activity peaks at different times within this period. Average rates suggest 11h UT, which is the same peak solar longitude (sol=235.17) as in 1996. Based on the data available, it is not possible to recognize double peaks or filamentary structures. The scatter and temporal variations are assumed to be caused by the poor conditions we had to face this year.
We gratefully thank all the observers who made their observations available by sending them to the Visual Commission or publishing them on one of the meteor mailing lists.
Abdo Sana'a (Jordan) Johannink Carl (the Netherlands) Al-Alwanew Mohammad (Jordan) Langbroek Marco (the Netherlands) Al-Mualla Ramez (Jordan) Lukic Vladimir (Yugoslavia, obs. USA) Al-Niamat Ahmad (Jordan) Lunsford Bob (USA) Assmus Joseph (USA) Miskotte Koen (the Netherlands) Brown Peter (Canada, obs. USA) Odeh Mohammad (Jordan) Collier Matthew (USA) Odwan Ibrahim (Jordan) Dalee Hani (Jordan) Sanchez Javier (Spain) Davis Mark (USA) Stomeo Enrico (Italy) Gliba George (USA) Taibi Richard (USA) Gorelli Roberto (Italy) Togni Rocky (USA) Gramer Lewis (USA) Trigo Josep M. (Spain) Hally Wayne (USA) Yrjola Ilkka (Finland) Haver Roberto (Italy) van Weerden Anne (the Netherlands) Hernandez David (Spain) Zay George (USA) 1997 Nov 17 --------------------- Time Sollong ZHR +- (UT) (J2000) --------------------- 0130 234.77 33 4 0400 234.87 35 7 0600 234.96 41 27 0815 235.05 66 31 0950 235.12 77 30 1050 235.16 132 43 1150 235.20 71 30 1250 235.24 95 33 2300 235.67 45 15 ---------------------
The ZHRs are calculated with a population index of r=2.0 and a zenithal exponent of 1.0. A large relative scatter of rates appears at the interface between observations from the Canary islands and North American east coast observers, indicating a zenithal exponent different from 1.0. Errors are the standard deviations of the average.
Rainer Arlt, 1997 November 22.
Visual Commission
International Meteor Organization
email: visual@imo.net
Homepage: http://www.imo.net
