Leonids 1996: the Hunt for clear skies...

Leonid filament & dust trail encounters in 1996

Leonid-filament:

Credits: Meteor Showers and Their Parent Comets, Peter Jenniskens, The Seti Institute, California

Dust trails: not expected, but maybe we detected a dust trail.


Picture 1 : Logo DMS crash expedition 1996 designed by Robert Haas.

Introduction
After the highly succesfull Leonid 1995 expedition in Andalusia (Spain), DMS started to make plans for a second expedition in 1996. Target: again Andalusia. In September 1996 it turned out that an expedition such as in 1995 could not continue. So Delphinus teammembers Casper ter Kuile, Marco Langbroek, Robert Haas, Jos Nijland, Marc de Lignie and myself, decided to stay in The Netherlands and organize a last-minute campaign to a place with clear skies somewhere in western Europe. During this campaign we had some help from KNMI meteorologist Jacob Kuiper, who tried to guide us to clear weather. And despite the very bad weather conditions in Western Europe, Jacob managed to guide us to an area were we had some clear periods and had some very interesting observations! Thanks Jacob! This years conditions: no moon interference (+30% moon).

Clear nights in the Netherlands!
The nights before the Leonid 1996 maximum were clear in the Netherlands. Both 13/14 and 14/15 November 1996 provided clear skies. The second night I observed a nice orange –4 Taurid. The same day Casper rented a camper, so we were able to drive to a good location and get some sleep before returning home. Unfortunately the weather changed on 15 November. Clouds were moving in from the east.

15/16 November 1996: hunt for clear skies part 1
In the evening of 15 november the sky was clear over the Netherlands. However, on the Internet we saw pictures from weather satellites: a massive cloud region in eastern Germany moved into the eastern parts of the Netherlands. It seemed to us that the northern parts of the Netherlands would remain clear. We decided to go to the village of Benningbroek, where Jos Nijland lives. When we arrived there, we were just in time to see the clouds moving in from the east. This is the signal for Jos and Marc to give up, but Robert, Casper, Marco and I wanted to make an ultimate attempt to go to Northern Friesland. So we went even further north and then drive east (driving on the Afsluitdijk) to Friesland. There, in the vicinity of the village of Sexbierum we found a fine location to observe the Leonids. It was situated a couple of hundreds meters away from the Waddensea, where we had a very clear sky with limiting magnitudes up to 6.8. When we started to observe, the Leonid radiant was just above the eastern horizon.
We continued observing for 2.5 hours, before the clouds came in. We observed a normal Leonid display during this short period. The Taurids put up a fine show this night: at 01:07:30 UT a –10 Taurids set the eastern horizon on fire in a bright flare of light! It left a persistent train of 11 seconds.


Picture 2: Camper at Sexbierum. Photo credits: Casper ter Kuile

16/17 November 1996: hunt for clear weather part 2
After a short nap in the camper we decided to go to Caspers home at De Bilt to obtain information from internet sources as well as consulting Jacob Kuiper to determine where to go to next. Unfortunately the forecasts were a disaster: a huge front was situated above southern Norway , Benelux country's, France and to the south of Spain! And the eastern parts of Europe were also clouded. Jacob predicted some clear spells near Calais. But don’t expect a full clear night he said! The teams split up: Casper, Robert, Marco and I (team Delphinus) are leaving with the camper, while Marc and Jos would take the Opel Astra (hence we called them "Team Astra”)
So, after renting a second generator (a necessity for the photographic and video equipment), we left De Bilt at 12:00 UT. The sky turned gray at that time… We continued through Belgium and encountered some bright intervals near the French border. However,near the city of Duinkerken we ran into very thick fog. Fortunately, when we arrived at Calais the fog disappeared and both teams met again in a roadside restaurant. There we consulted Jacob: “Stay in this area, there are some clear spells over the Channel and maybe they will move inland”. The best chance we would stand at Le Havre. Le Havre was certainly 150 to 200 miles away at that time and too far away. We have to drive hours before we would reach Le Havre. So we dicided: team Delphinus headed to a clear place south of the river the Somme and Team Astra would stay north of the Some.

When we left Calais we ran into thick fog again. After an hour of desperately searching for clear skies, we suddenly found ourselves in a clear spot near the small village of Brutelles. Then we took a dirt road up on a hill and inspected the sky. It was clear, but in every direction fog was visible. We drove a bit further, but unfortunately we drove back into the fog... After another hour of driving through this fog, we headed back for Brutelles, hoping to return to that clear spell we found earliër. Luckily it was still clear in Brutelles. From there we drove uphill to the east. On a newly ploughed meadow we found a suitable spot. Quickly we unloaded the van, starting up the generator, setting up the camera equipment and unfolded the stretchers. Fifteen minutes later, everyone was ready to observe the Leonids!

Casper and Robert were taking care of the photographic equipment. Marco and I started visual observations at 23:40 UT. The sky was very clear (lm 6.9) but at low altitude there was some haze. After a while the lm dropped to 6.3 and after 00:35 UT clouds moved in. Despite the low altitude of the Leonid radiant we did see relatively many Leonids withs some bright ones up to –2.

The team then decided to sleep in the camper. I stayed awake and every 10 minutes I looked out to see if it was clear. 03:00 UT: a phone call from Team Astra: they found clear skies and were observing the Leonids at that moment! Luckily, at 03:15 UT the cloud cover at our own site was dissolving and disappeared completely after a while. At 03:26 UT, observations started again and that was the beginning of a beautiful meteor show.

Many bright (and weak) Leonids!
When Marco and I started the observations, we noticed that, contrary to 1995, a large number of faint Leonids were visible. But also many fireballs!
03:40 UT: -4 Leonid, Orion, train 11 s.
03:57 UT: -2 Leonid, Auriga, train 8 s.
04:08 UT: -3 Leonid, Draco, train 10s.
04:12 UT: -2 Leonid, Virgo, train 6 s.
04:13 UT: -1 Leonid, Perseus, train 4 s.
04:22 UT: -6 Leonid, Eridanus, train 20 s.
04:24 UT: -1 Leonid, Ursa Major, train 3 s.
04:29 UT: -3 Leonid, Eridanus, train 6s.
04:32 UT: -4 Leonid, Orion, train 4 s.
04:32 UT: -4 Leonid, Orion, train 4 s.
04:32 UT: -4 Leonid, Eridanus, train 5 s.
04:37 UT: -3 Leonid, Leo, train 5 s.
04:48 UT: -3 Leonid, Bootes, train 4s.
04:53 UT: -3 Leonid, Bootes, train 3 s.

We could observe untill 04:55 UT when clouds moved in very fast. It struck Marco and me that in the last half hour more and more faint Leonids were active. After a final short period of clear weather (05:40-05:54 UT during dusk) we stopped our observations. We drove to a road-house for food and a bit of sleep. Then we drove back to De Bilt. After cleaning out the camper we traveled back to our homes. Happy because we had seen our second Leonid outburst!
A few days later, when Marco analyzed our data, he found that we had observed a short peak of weak Leonids. This short peak of weak Leonids appeared on top of a component (the filament structure) with bright Leonids (ZHR 60), in total the ZHR would be ~140. When Marco announced our results and observations at the Internet, more observers found a peak of Leonid activity at the same time. It is still not clear to what structure this weak Leonids belongs to. The graph looked like a dust trail passage, but there are no predictions for dust trail encounters for 1996. The bright Leonids were belonging to the old "filament" structure of comet 55P/Tempel-Tuttle.


Picture 3 : ZHR curve of the Leonids 1996 as observed by DMS members during the night 17/18 november 1996. The ZHR curve is publised in:
Leonid outburst activity 1996: A broad structure and a first occurrence of a narrow peak of fainter meteors
.
This article was written by Marco Langbroek for Meteoritics & Planetary Science, vol. 34, no. 1, pp. 137-145 (1999).

The Astra Team: what did they see?
Unfortunately they had only a short spell of 40 minutes, prior to our period of clear sky. So they did see some nice Leonid fireballs, but not the faint Leonids component. Also, there are no simultaneously photographed meteors.

Other Leonid observations in 1996.
18/19-11-1996
21/22-11-1996

[1] Leonid outburst activity 1996: A broad structure and a first occurence of a narrow peak of fainter meteors. Langbroek M., Meteoritics & Planetary Science, vol. 34, no 1, pp. 137-145 (1999).

 

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