Orionids 1993: visual observations (I)

Unusual high meteor-activity at october 17/18 observed by Koen Miskotte

Dutch Meteor observer Koen Miskotte from Harderwijk (The Netherlands) reports unusual high activity of the ORIONID-meteorstream during the night of october 17/18 around 01-02 h UT. According to his observations the activity of the stream, commonly associated with comet P/Halley, has been a factor 5 (five) higher than normal at given solar longitude, and even considerably higher than normal activity around date of maximum (which is october 21/22, so four days after the reported high activity).

Observing under good sky conditions (sky limiting magnitude +6.6), Koen observed absolute numbers of 13 Orionids in 55 minutes around 00:30 UT, 23 in 51 minutes around 01:30, 25 in 60 minutes around 02:30 and 20 in 60 minutes around 03:30, with radiant heights of resp. 33, 41, 47 and 51 degrees.

Corrected for radiant height, limiting magnitude and personal perception coefficient and working with the normal Orionid population-index r=3.1 (note however the remarks about meteor brightness later in this bulletin...) this gives the following ZHR-results:

UT                    sol. long.              ZHR            +/-
00:30                 204.734                 19             5
01:30                 204.775                 31  (!)        6
02:30                 204.816                 25             5
03:30                 204.857                 19             4



At this moment, Koen seems to be the only person who observed during the night 17/18 at least in the Netherlands. Activity during the next night (18/19) seems to have been quite NORMAL.

Data Koen Miskotte:

UT                     sol. long.             ZHR           +/-
01:30                  205.768                15            5
02:30                  205.809                13            5
03:40                  205.851                13            3

..and a combination of data from Koen and undersigned (-Voorschoten): 01:30 UT 19 +/-8, 02:30 UT 17 +/-7, 03:40 UT 14 +/-6. Note however, that my observations were done under not too favourite conditions, so Koen's observations alone may actually give the more accurate results. Normal ZHR-value for this solar longitude is around 14, in good accordance with the observations.

Normally, the Orionids peak around solar longitude 208.7 which is october 21/22 at 0h UT this year, with a maximum ZHR of about 22. The stream has a quite broad maximum with ZHR above 20 between october 20 and 24.

Another unusual aspect reported by Koen is the appearance of quite a number of very bright Orionids during the night 17/18. Koen reports a -5 magnitude Orionid fireball, a -4 and two of magnitude -3. This is very unusual since Orionids usually are quite faint (population-index 3.1) and seldom give meteors brighter than -1!

One does not expect serious enhanced activity from the Orionid-stream. The stream is an 'old' stream, with meteoroid particles in well diffused orbits, the parent comet (P/Halley) at present has an orbit which seems too far from earth orbit for a possible encounter with a 'fresh' dustconcentration. This makes, that we are really surprised by the observed high activity (and why so far from the 'normal' peak in sol. long.?!?).

Normally, I should be very suspicious toward a report by only one observer under these conditions. However, I know Koen Miskotte as an extremely reliable, well-experienced, accurate and faithful observer (he is by far number 1 in the Dutch top ten of observers -based on number of observing hours per year- for several years now, and started serious meteor work in the early eighties), so I can do nothing else than give his report full credit.

There seems little doubt that it was the Orionid-stream displaying the strong activity and not another radiant. The Epsilon-Geminid radiant is active around october 20, but with some care these meteors are distinguishable from Orionids (and in fact they were noticed by Koen, with a normal ZHR of about 2-3).

Given the totally unexpected character of the event, and the fact that we have only one observation (though a very reliable one), we would like to make a strong call for other observations to be reported, to see if they confirm the enhanced activity or not.

Marco Langbroek
(Dutch Meteor Society)
Jan Steenlaan 46
NL-2251 JH Voorschoten
The Netherlands
Telephone +31-71-613750
E-mail webmaster@dmsweb.org or betlem@strw.leidenuniv.nl

Address Koen Miskotte:
Westrak 53
NL-3844 LD Harderwijk
The Netherlands

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back.gif This page was last modified on October 21, 1993 by
Casper ter Kuile and Marco Langbroek