Dutch Meteor Society: Leonids 1998 Results

23 Янв 2014 | Author: | No comments yet »

Observations of the Leonids started on 16 November at 21h UTC. The first long-duration echo (4 minutes) was registrated at 21h26m UTC, almost exactly at the moment of the calculated rise of the radiant for the midpoint between Roden and Wroclaw. Soon after radiant rise the number of long-duration echoes started to increase. Such echoes are typical for the Leonid meteors with their high velocity of about 70 km/s. Counting the number of echoes of Leonids is difficult because of their long-duration and strong overlap. A probably better indication for the activity of the Leonids is the total reflection time. In figure 1 the percentage of hourly elapsed time of signals stronger than 0.1 mV is given. The figure shows that during many hours the stations around 72.11 MHz were received almost constantly. Peak activity was observed around 5h UTC, while after 10h the activity declined rapidly. The numbers are more or less proportional with the sine of the elevation. If the sine function is a valid representation for the observability of overdense reflections, then the Leonids had a rather flat activity distribution. For comparison the total reflection time is given for three consecutive days, starting 16 November 1998.

The hourly counts of meteors stronger than 0.1 mV is given in Figure 2. From this figure, and also from recorder charts, it is clear that the number of counts dropped by about 50% between 23h00m and 3h30m UTC. Probably one or more of the transmitters were shut down or power was reduced. A provisional correction has been applied for this effect in Figure 1 (dashed line for 16/17 November). After this correction the activity is more pronounced between 0h and 2h UTC. In Figure 2 also the hourly counts for 7/8 November 1998 are displayed as indication of the normal sporadic activity.

Wim Zanstra


Everybody could hardly wait for the maximum of the Leonids that should take place in the night of November 17 to 18 1998. At clear skies there should be a possibility that also in western Europe this famous meteor shower could be observed. The moon would not disturb this time. Important astronomers did there best to make clear that everybody should look at the coming heavenly fireworks. In my particular case the shower should be observed by means of the reflections of radiowaves, so independent of clouds and disturbing light. As emitter we used radio Wroclaw at the frequency of 72.11 MHz. Only the height of the radiant above the horizon and much less the azimuth should determine the possibility to detect a meteor. While it always is wise to begin observations one or two days before the (expected) maximum the action was started at November 16, 22 UT after the rise of the radiant. The figures allready show at that moment a high activity with a lot of longer reflections. If this were a sign for the real maximum that should occur during the next night, it was very promissing. The break from 3 till 9 UT was well used to come in a good shape for the real work in the night of November 17/18.

Azimut 110

During the morning at November 17 the activity, especially of the longer reflections, was still very high. After the setting of the radiant at about 14 UT no reflections could be received anymore, and preparations for the coming night began!

Figure 1. The total hourly rates per hour of the Leonids (n), corrected for the sporadic background, reflectiontime and breaks, are following the height of the radiant (h,%) very well. It shows a rather flat activity pattern, exept at the beginning of the observations. The activity of the Leonids must have been relatively higher there. At the end of the 17th of November the activity was almost reduced to zero again.

Figure 2. The hourly rates per hour of a number of different kinds of reflections, corrected for reflectiontime and breaks. Clearly seen is the dominant behaviour of the long signals, which practically only belong to the Leonids.

Figure 3. The reflectiontime in percentages of one hour (tc) and corrected for the messured reflectiontime and breaks. This one as well follows the height of the radiant (h,%) and disappears to the end of November 17 practically completely.

Azimut 110

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