On several occasions ([1],[2]) I have introduced our video system *MOVIE* and the way it
works. I was able to show quite impressive meteor videos and described the used hardware.
Finally first results from the analysis of video meteors were presented on last years IMC ([3]).

Since then we had some more successful video observation sessions and did a lot of new
investigations with the video data. This January we observed the Quadrantids near Hannover
(Germany) and recorded more than 100 meteors parallel to our visual observations on video
tapes (among them a nice -4 mag Delta Cancrid in CMa) with *MOVIE* ([4]). In the following
weeks I did the tremendous work of analysing the Quadrantid tapes as well as the Perseid
video from August 11/12, 1993, which was still unanalysed up to that time. There were
another 250 meteors on these tapes, recorded during 7 hours of observation in the
Schwarzwald mountains (Germany). After finishing this (all video data are now stored in *PosDat*
format and available for every interested observer from Visual Commission Director
Rainer Arlt) I had the necessary data basis for interesting research work in different fields of
meteor astronomy and did some first calculations. The results were presented at the annually
meeting of the German Meteor Observers Society (AKM e.V.) in Kirchheim (March 1995),
here follows a summary of the most interesting outcomes.

One of the main aims of our video work is the accurate determination of radiant positions
connected with the search for sub-radiant structures. In Belogradchik I present a first radiant
plot for the Perseids 1994. Unfortunately bad weather conditions last year lead us to record
most meteors far away from the radiant in the summer triangle and only very few in other
region such as Andromeda/Pegasus. So the resulting plot ([3]) showed only a longish,
inaccurate maximum near the predicted radiant position. There was no reliable statement possible,
whether or not the are faint structures in the shower radiant of the Perseids.

This year we planned to observe the Quadrantids at a distance of about 30° from the
radiant, because we wanted to obtain precise double station video observations together with
our Dutch friends from the NVWS. Unfortunately the weather stopped our observation with
clouds early in the morning and a guy called Murphy did the rest of the job: We had to finish
just at the time, when the second video team 20 km away restarted their observation after their
sky became clear. Thus we again did not managed it to record double station meteors. In addition
our mounting did not drive the video system, because it was too cold (-8° Celsius). This is
why the radiant slowly rotated into the field of view, and we captured many short meteors
around the radiant. Last but not least someone stumbled in the middle of the night over a
power socket, which caused the lens heating stop to work. Even though the resulting ice layer
on the lens became thicker and thicker with time, it finally was a quite successful observation.
We found almost 80 Quadrantids on the video tapes and could produce a nice radiant plot for
this shower. **Figure 1** shows this plot using the *tracing* method of Rainer Arlt's *RADIANT*
software, **figure 2** contains the same 39 meteors using the *intersection* method. This means,
that complete meteor trails are traced back to the radiant in the first image, whereas the second
picture shows only all the intersection point between two distinct meteor tracings.

Figure 2 - radiant plot for the '95 Quadrantids using the intersection method

It is obvious, that the 'theoretic' position of the radiant (shown as a green circle with a diameter
of 5°) given in the IMO publications is very good. Furthermore there is no sub-radiant
structure visible, even though the plot is very accurate and could show such features. So
the absence of distinct structures within the Quadrantids radiant at the level of about one
degree is the main result of this analysis.

As usual I tried to produce a nice picture of the shower (**figure 3**), which looks quite different
from the Perseid image I presented last year (**figure 4**) at the IMC.

Figure 4 - shower picture of the Perseids

The meteors near the radiant are very short, we even recorded two pointlike meteors, which
did not move at all.

In addition to this image I produced a computer animation, that shows the meteors appearing
and disappearing dynamically around the radiant of the Quadrantids. During a few seconds 18
meteors with different lengths, velocities and brightness are visible on the screen, which illustrates
all the well known effects of meteor showers quite impressive. After I have converted
this animation into a standard format, I will make it available to everybody interested in it via
my WWW homepage or by other means.

The next interesting shower have been the Perseids. It took me several days to analyse all the
meteors from their maximum night '93, but then I had a database with more than 300 shower
meteors available. In contrary to last year almost all meteors in 1993 were recorded in the
morning hours and came from the Andromeda/Pegasus region, so the data sets from both years
complement one another very good. The accuracy of parts of the data is not as good as for the
Quadrantids, because I used an earlier version of the analysis software last year. In return I had
a factor of ten more meteors available for the radiant plot. **Figure 5** gives the distribution of
228 Perseids around the radiant. Their mean distance from the radiant is obviously still quite
large, the violet ring marks a distance of 100° from the centre. **Figure 6** and **7**
show the radiant plot for these meteors again using the *tracing* and *intersection* method of
*RADIANT*.

Figure 6 - radiant plot for the Perseids using the tracing method

Figure 7 - radiant plot for the Perseids using the intersection method

The meteors scatter more around the radiant, so the resulting peak is not as sharp as for the
Quadrantids. The mean position of the radiant fits again quite well with the data given in
IMO's meteor shower list. There are some minor sub-radiant structures visible in the plot, but I
do not believe in the significance of these irregularities. The positional accuracy of each single
meteor was only 1-2° near the radiant and the distribution of the meteors is still not optimal.
So these structures are most probably artefacts.

One more interesting fact is the good agreement in the radiant position using two different
methods (tracings/intersections). It seemed to me, that especially for higher numbers of
meteors the later method gives better results, but both of them are equivalent on a first
glimpse. Only the radiant position obtained using the *probability* algorithm shows a bigger
difference, which is a subject of further investigation.

Beside the determination of radiant positions also ZHR calculations are an interesting area for
video observers as shown on the last IMC. Some strange effects like abnormal high meteor
rates during twilight were found at the first analysis but not confirmed yet.

The determination of zenith rates for this years Quadrantids was especially complicated due to
the mentioned 'frozen lens' and the resulting large drop of the systems limiting magnitude.
Nevertheless Jürgen Rendtel and I could show ([5]) a good qualitative correspondence of
visual and video rates near the maximum. There is for instance a narrow peak in both activity
graphs at 23:15 UT, which lasted only about 20 minutes.

One of the most interesting topics for me is the search for meteor clusters. In a paper from
1992 ([6]) I had analysed our visual meteor observations from that year searching for cluster
effects and found absolutely nothing. Even though we had a good data basis (several hundred
meteors observed from three visual observers in six successive nights with a time accuracy of 1
second) due to our computer based observation ([7]), the distribution of the meteors matched
exactly the one expected for randomly in space distributed particles.

Two month ago I repeated this calculation for our video observation of the Perseid maximum
night '93. This time I had to apply a special transformation first, because the standard formulae
works only for constant meteor activity. This was definitely not given a few hours before the
sharp ZHR peak. Using the same time resolution as for the visual analysis in 1992 I found
again no evidence for any type of clustering ([8]). **Figure 8** gives an idea, how good the theory
for randomly distributed particles (exponential distribution) fits the observational results. The
distance between two successive meteors is plotted on the x-axis, added up in intervals of 20
seconds length. The y-axis gives the percentage of each class compared to the whole number
of 337 pairs of meteors.

My suspicion now was, that clustering appears only on very short time scales (1-2 seconds),
which might be smeared out in the 20 second intervals given above. So I did another calculation
with an interval length of only one second, that is presented in **figure 9**. Here I used
cumulative intervals to have more meteors in each class and get better statistics by it.

Again one can clearly see, that there is almost no difference between (clusterless) theory and
video observation. But if you look close enough to the very first intervals (up to a time distance
of 12 seconds) you will see, that the observation shows always slightly more meteor
pairs than expected! To make this clearer I added another graph to the diagram, which represents
the relative differences between both values. We find a surplus of 57% in the first
(meteor distances less or equal 1 second) and more positive differences in the following intervals. This
implies, that there really might be some type of clustering of meteors at the Perseid maximum.

Looking at the statistics we should not forget, that this is a weak first clue: 57% surplus simply
means, that we observed 11 pairs of meteors instead of 7 expected from theory. 30% surplus
of meteor pairs with less or equal than 3 seconds distance stands for 21 pairs instead of 16,1.
Furthermore I had to apply the mentioned special transformation for variable ZHR, which
makes the results even more inaccurate. At least we have here for the first time a quantitative
indication for a cluster effect at a low level of about 1.5%. This number results from additional
computation to find the best fit between observation and theory and should be regarded as a
dimension for the phenomenon only. All values between about 0.5% and 3% are thinkable too,
because the calculations were quite unstable in relation to the used interval length and model.

Again the data basis is still not complete enough to give more precise statements at this time.

There are other interesting effects, which have to be confirmed in the future too. In Belogradchik
I showed, that visual observers regularly underestimate meteor brightness by about 1
magnitude ([3]). A possible explanation is, that we estimate the brightness from the impression
of the whole meteor trail, whereas video systems determine it at a scan rate of 25 measurements
per seconds and therefore really obtain the absolute maximum brightness. This effect
was dominant during the latest analysis of the Quadrantids and Perseids too, but I have not
done another quantitative calculation yet.

Our latest video data provide a good basis for statistical analysis of meteor light curves along
their path. This work remains for the next months as well.

To sum it up it can be said, that video systems have again proved to be very powerful tools in meteor observation. They provide large amounts of accurate data as a basis for many different investigation.

Proceedings of the International Meteor Conference 1993, p.71

[2] Molau, S. (1995), "Videobeobachtung von Meteoren",

Sterne und Weltraum 34-7, p.554, 34-8/9, p.666

[3] Molau, S. (1994), "

Proceedings of the International Meteor Conference 1994, p.51

[4] Molau, S. (1995), "Auf Sternschnuppenjagd in Niedersachsen",

Mitteilungen des Arbeitskreises Meteore 20-3, p.4

[5] Molau, S. and Rendtel, J. (1995), "Quadrantiden 1995 - noch ein Rückblick",

Mitteilungen des Arbeitskreises Meteore 20-4, p.3

[6] Molau, S. (1992), "Murphy's Effekt bei der Meteorbeobachtung?",

Mitteilungen des Arbeitskreises Meteore 140, p.5

[7] Nitschke, M. (1991), "Computer-Based Meteor Observation",

Proceedings of the International Meteor Conference 1991, p.54

[8] Molau, S. (1995), "

Mitteilungen des Arbeitskreises Meteore 20-1, p.6

Sirko Molau; last change: July 18, 1996