Leonids rose to the occasion — despite bad weather
During the nights of 16-17 and 17-18 November, Joe Zender and Detlef Koschny of ESA’s Space Science Department at ESTEC attempted to obtain ‘stereo’ observations of the Leonid meteors with image intensified video cameras. These cameras are equipped with wide-angle lenses and can record meteors that are too faint to be seen with the naked eye.
It was hoped that the various observing teams would be able to obtain parallel observations from four different locations 70 km to 100 km apart. Zender was observing with a team from the Dutch Werkgroep Meteoren at Hogersmilde in the Netherlands. Unfortunately, poor weather only allowed his team to record about 1.5 hours of video data outside the time of the maximum activity.
Other teams had a little more success. On the night of 16-17 November, two stations succeeded in observing simultaneously: Henry Henriks (Werkgroep Meteoren) located at the Heest Observatory and Joost Haartman, Michiel Brentjens and Roy Keeris (Werkgroep Meteoren) located near Almere at the Groene Kathedraal, were able to observe with the video cameras for about 4 hours. However, activity was moderate and no dedicated peaks or events could be reported.
On the next night, the team in Hoogersmilde was able to observe under good conditions until 00.15 UT. When the clouds and rain closed in, they were able to dismantle their equipment and rapidly move to a relatively cloud-free area near Groningen. The camera equipment was set up again by 03.20 UT, about 20 minutes before the predicted peak. Despite problems with the clouds and Moon, they were able to observe increasing activity, with about 30 meteors in the first hour. Overcoming more disruption from the weather, the team was able to recognise another spell of increased activity at about 04:45 UT. Visual and camera observations continued until 06.30 UT, with another suggestion of increasing activity before dawn (from 05.30 UT to 06.15 UT).
Koschny’s attempted observations in the Harz mountains of Germany were also plagued by bad weather. Apart from two sporadic meteors seen from the Max-Planck-Institute in Lindau-Harz on 17 November, there was nothing to report.
Simultaneous observations from different sites were not possible on the second night due to the continually changing location of the teams, but it is hoped that analysis of the videotapes will give a better idea of the ZHR (zenithal hourly rate) values. Everyone is hoping for better luck with the video observations next year!
Echoes of the Leonids
Jean-Pierre Lebreton and Trevor Sanderson from ESA’s Space Science Department at ESTEC used radio signals rather than telescopes or cameras to observe the elusive meteors. Their technique used the ability of plasma (ionised gas) clouds around glowing meteor trails to reflect radio waves.
The BBC helped the experiment by transmitting from Woofferton until 06:00 UT (7 Local time), and then switched to its normal transmission schedule (from Cyprus between 06:00 UT and 08:00 UT, and then from both Woofferton and Skelton from 08:00 UT onwards).
The radio recordings were excellent, with numerous very unusual echoes which can be attributed to the Leonids. Preliminary analysis of the High Frequency night-time radio observations indicates that the (non-sporadic) activity increased significantly on 18 November, but it seems there was some activity 1-2 days before (16 and 17 November), and perhaps 1 day after (19 November).
A rise in activity was noticeable on 18 November between 03:00 and 05:00 UT, and also from 07:00 UT onwards. Few daytime echoes could be detected during the transmission from Cyprus as the geometry was unfavourable. However, the activity at around 09:00 on 18 November was much higher than on the days before or after.
Despite pouring rain until 01:30, the team also managed to capture a few meteors against the bright Moonlit background on a video taken with a standard CCD camera. Some of the Leonids displayed impressive trails that lingered for a few seconds.
24 hour plots have been produced for the following 3 days : 17 November, 18 November, and 19 November. A reference plot, (when the BBC transmission was OFF over night) was also produced for 12 November.
Tell-tale Flashes on the Moon?
HÂkan Svedhem of ESTEC’s Science Department used a 25 cm telescope and a video camera to observe the dark hemisphere of the Moon on the nights of 16-17 and 17-18 November, in the hope of seeing some Leonid meteors impact on the dark part of the Moon.
The search for impacts is a difficult, time-consuming business, since a flash typically lasts for only one or two video frames. Expectations were also limited since most impacts were predicted to occur on the lunar far side, and only a very small visible area at the Moon’s northern cusp was exposed to the meteor stream.
Problems with condensation on the lens forced Svedhem to stop at about 05:40 UT on 17 November — unfortunate timing, since predictions indicated that the Moon would pass close to the 1932 dust stream at that time.
The next day proved more rewarding, and he was able to observe the Moon from 02:19 UT onwards. After preliminary computer analysis of the videotape, Svedhem has so far found one unquestionable flash of light from an impact that took place at 05:42 on 18 November, but the search goes on as he continues to compare consecutive frames and filter out background "noise".
USEFUL LINKS FOR THIS STORY
* Leonids 2000: ESA observation reports
http://sci2.esa.int/leonids/leonids2000/report.html#listen
* Listening to the Leonids
http://helio.estec.esa.nl/sound.html
* More images and sounds files of the Leonids
http://solarsystem.estec.esa.nl/planetary/radiometeor.htm
IMAGE CAPTIONS:
[Image 1:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=1&cid=12&oid=25781&ooid=18305 ] Composite image of 6 Leonids meteors.
[Image 2:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=1&cid=12&oid=25781&ooid=25861] Comet C/1999 S4 (Linear), 28 June 2000.
[Image 3:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=1&cid=12&oid=25781&ooid=25860] Radio recordings made on 12 November 2000 without a BBC transmission and before the Leonids appeared. Each panel represents 2 hours and cover 25 Hz in frequency. Note that high frequencies are at the bottom and lower frequencies at the top of the panel. For reference, a 1Hz Doppler shift at 17640 kHz (carrier frequency for the BBC transmission) is caused by a Doppler velocity of ~ 17 m/s.
[Image 4:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=1&cid=12&oid=25781&ooid=25856] 24 Hour radio recordings of the Leonids on 17 November 2000. Each panel represents 2 hours and cover 25 Hz in frequency. Note that high frequencies are at the bottom and lower frequencies at the top of the panel. For reference, a 1Hz Doppler shift at 17640 kHz (carrier frequency for the BBC transmission) is caused by a Doppler velocity of ~ 17 m/s.
[Image 5:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=1&cid=12&oid=25781&ooid=25858] 24 Hour radio recordings of the Leonids on 18 November 2000. Each panel represents 2 hours and cover 25 Hz in frequency. Note that high frequencies are at the bottom and lower frequencies at the top of the panel. For reference, a 1Hz Doppler shift at 17640 kHz (carrier frequency for the BBC transmission) is caused by a Doppler velocity of ~ 17 m/s.
[Image 6:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=1&cid=12&oid=25781&ooid=25857] 24 Hour radio recordings of the Leonids on 19 November 2000. Each panel represents 2 hours and cover 25 Hz in frequency. Note that high frequencies are at the bottom and lower frequencies at the top of the panel. For reference, a 1Hz Doppler shift at 17640 kHz (carrier frequency for the BBC transmission) is caused by a Doppler velocity of ~ 17 m/s.
