(meteorobs) Analyzing 6 hrs of Perseids video from Romania
Daniel Fischer
dfischer at astro.uni-bonn.de
Tue Aug 17 13:20:47 EDT 2004
Mintron video observations of the Perseids 2004
from Romania, in the nights before & after the maximum
Or: Tracking down an invisible outburst ...
The skies were excellent in these (and only these!) two
nights, with a limiting visual magnitude beyond 6.2. A
few cloud fields blocked parts of the sky early on Aug.
13, then went for good, but the 55-degree field of view
of the camera (that was changed frequently during the
nights) with its 6 mm f/0.8 lens was always completely
free of substantial obstructions of any kind.
Column 1 is the Universal Time if the beginning of each
5-minute interval; local time was UTC+3 hrs.
Column 2 is the approx. altitude of the radiant as
calculated with Redshift (substituting SA= 23662 and
other nearby stars).
Column 3 is 1/sin(radiant elevation), a correction
factor that must be multiplied with the detected number
of meteors to get the true rate one would see if the
radiant were in the zenith ("zenithal rate").
Column 4 is the number of Perseids detected per 5-minute
interval by watching the tapes on TV screens. A "< >"
around the number means that it is an extrapolation
because not the full five minutes were recorded on tape.
Column 5 is that number multiplied with the correction
factor to get the true Perseid rate; since I have no
clue (yet) if and how other factors such as the Mintron
integration factor (that was set between 8 and 24
frames), the sky quality, the direction of looking etc.
further influence the result, this is the only
correction applied.
To see the ASCII graphics properly you must view this
message with non-proportional characters, e.g. Courier!
The left plot is the value of column 5 - vividly
demonstrating the stochastical nature of meteor
appearances in the sky during a major shower.
The right plot shows a simple sliding mean of the values
of column 5; it is usually (previous + this + the next
interval)/3, except for the first and last value of each
sequence when it is (this + the next or the previous
interval)/2.
August 11/12, 2004
Corbasca, Romania, 27 08 East / 46 15 North
UTC Alt(R) Cor. Per Per x Corr. Sliding Mean
19:30 25.0 2.4 1 2 |** |*
19:35 25.3 2.3 0 0 | |**
19:40 25.6 2.3 2 5 |***** |**
19:45 26.2 2.2 0 0 | |***
19:50 26.6 2.2 2 5 |***** |**
19:55 27.0 2.2 0 0 | |**
20:30 30.0 2.0 2 4 |**** |*****
20:35 30.6 2.0 3 6 |****** |******
20:40 31.2 1.9 4 8 |******** |********
20:45 31.5 1.9 5 10 |********** |*******
20:50 32.2 1.9 1 2 |** |******
21:45 38.5 1.6 1 2 |** |**
21:50 39.0 1.6 2 3 |*** |**
22:20 42.5 1.5 1 2 |** |**
22:25 43.2 1.5 1 2 |** |***
22:30 43.7 1.4 3 5 |****** |****
22:35 44.5 1.4 4 6 |****** |*****
22:40 45.0 1.4 2 3 |*** |*****
22:45 45.6 1.4 4 6 |****** |****
22:50 46.3 1.4 2 3 |*** |*****
22:55 46.9 1.4 5 7 |******* |*****
23:15 49.4 1.3 <4> 5 |***** |*****
23:20 50.0 1.3 3 4 |**** |***
23:25 50.7 1.3 1 1 |* |***
23:30 51.5 1.3 3 4 |**** |****
23:35 52.0 1.3 5 6 |****** |****
23:40 52.7 1.3 2 3 |*** |*****
23:45 53.4 1.2 5 6 |****** |****
23:50 54.0 1.2 2 2 |** |***
23:55 54.7 1.2 2 2 |** |**
00:00 55.3 1.2 2 2 |** |****
00:05 56.0 1.2 6 7 |******* |***
00:10 56.6 1.2 1 1 |* |***
00:15 57.3 1.2 1 1 |* |*
00:30 59.2 1.2 2 2 |** |***
00:35 60.0 1.2 3 4 |**** |***
00:40 60.5 1.1 4 4 |**** |****
00:45 61.2 1.1 3 3 |*** |***
00:50 61.9 1.1 2 2 |** |****
00:55 62.5 1.1 5 6 |****** |****
01:00 63.2 1.1 3 3 |*** |***
01:05 63.8 1.1 0 0 | |*
01:10 64.5 1.1 1 1 |* |
01:15 65.1 1.1 0 0 | |*
01:20 65.7 1.1 1 1 |* |*
01:25 66.4 1.1 2 2 |** |**
01:30 67.0 1.1 <2> 2 |** |**
August 12/13, 2004
Darmanesti, Romania, 26 30 East / 46 20 North
19:30 24.9 2.4 0 0 | |***
19:35 25.3 2.3 3 7 |******* |***
19:40 25.8 2.3 1 2 |** |***
19:45 26.2 2.3 0 0 | |*
19:50 26.7 2.2 0 0 | |*
19:55 27.0 2.2 <2> 4 |**** |*
20:00 27.6 2.2 0 0 | |*
20:05 28.0 2.1 0 0 | |
20:10 28.5 2.1 0 0 | |*
20:15 29.0 2.1 1 2 |** |*
20:20 29.5 2.0 0 0 | |*
20:25 30.0 2.0 0 0 | |
20:30 30.5 2.0 0 0 | |*
20:35 31.0 1.9 1 2 |** |**
20:40 31.5 1.9 2 4 |**** |***
20:45 32.0 1.9 1 2 |** |****
20:50 32.6 1.9 3 6 |****** |***
20:55 33.1 1.8 0 0 | |**
21:00 33.6 1.8 <0> 0 | |
23:00 47.3 1.4 0 0 | |*
23:05 47.9 1.3 2 3 |*** |**
23:10 48.5 1.3 2 3 |*** |**
23:15 49.2 1.3 1 1 |* |***
23:20 49.8 1.3 4 5 |***** |****
23:25 50.5 1.3 4 5 |***** |*****
There is evidence in the video data from the 2nd
interval for enhanced activity over several tens of
minutes - something that was *not* noted as obvious by
any of the observers in Corbasca at the time (who were
very alert in that period) nor is manifest as a strong
increase in meteors per 5-minute interval on the Mintron
video. After all, the latter rate never exceeded 5 (i.e.
one Perseid per minute), a value that was reached again
and even exceeded a couple of times later that night.
The fact that no significant outburst was 'felt' at
Corbasca is also the reason why the recording was
stopped after the 20:50-55 UTC interval when a tape was
full: We all were pretty sure at that point that the
predicted extra-outburst had not happened, and I rather
repeated lengthy attempts to image the dust trail
directly in space then, with maximum integration and
also a longer focal length. (Excess faint meteors should
nonetheless have shown up on these videos as obvious
streaks - they didn't).
*Only* if one applies the correction for the radiant
altitude it becomes apparent that something moderately
unusual was going on from 20:30 to 21:00 UTC or so. But,
based on these video data alone, it really cannot be
called a major outburst, let alone mini-storm: The
smoothed zenithal video rate peaked at about 96 Perseids
an hour, while the zenithal video rate sustained for
many hours later that night hovered around 60 an hour
(and still was in the 30s to 40s one night later).
That's an increase of just 60 percent. Add to that the
apparent lack additional faint meteors that were
forecast but not seen visually or by video, and once
might conclude that the outcome of the Perseids 2004
dust trail studies was a rather mixed bag ...
Conclusion: I rather have meteor outbursts that one can
*see* immediately by looking at the sky and that blows
you away - such as fabulous 1993 Perseids, let alone the
1999 & 2001 Leonids - rather than this one which only
manifests itself after tedious mathematical analysis.
The community should come up with the different term for
these subtle rate enhancements and leave terms like
"outburst" for the *real* sky shows.
Daniel Fischer, Koenigswinter, Germany, Aug. 17, 2004
P.S.: Uninterrupted video coverage of the whole night
from Corbasca has been obtained by K. ter Kuile from the
DMS with an intesified camera, but the tapes have not
been analyzed yet (and are still travelling with him
through Romania). And several members of SARM did
systematic visual counts at the site (something I never
got around to do because if fiddling around with the
Mintron). Thus the shape and amplitude of the
'invisible' outburst should become better known in the
future, based on observations from Corbasca alone.
P.P.S.: The increase in Perseid detections in the very
last recording interval of August 12/13 deserves further
study - as the camera was looking towards the horizon
now instead of straight up as before. That change had
been necessitated by excessive dewing which suddenly set
in when outside, and so I had eventually retreated into
a building, having to work from a window. It is well
known (since the Leonid storm of 1999) that looking
towards the horizon increases the meteor detections a
lot WHEN DONE FROM AN AIRPLANE: Could it be that this
'Koschny effect' also applies to some extent to
groundbased video obervations with their enhanced Near-
IR sensitivity (as compared to visual observations where
looking low does not help)?
P.P.P.S.: I did some visual counting eventually during
the night of August 12/13 in Darmanesti, partly in
parallel with the video recordings, in 15-minute-
intervals. Being an inexperienced visual observer, my
perception factor is probably quite low but hopefully
constant enough:
20:00-20:15 5 Perseids (corrected: 10), one other
20:15-20:30 2 Perseids (corrected: 4)
20:30-20:45 2 Perseids (corrected: 4)
20:45-21:00 8 Perseids (corrected: 15), one other
21:00-21:15 4 Perseids (corrected: 10)
21:15-21:30 8 Perseids (corrected: 15)
The corrections are for the radiant elevation and -
additionally in interval # 5 - for 4 minutes spent not
looking. The zenithal limiting magnitude, as determined
from the IMO counting fields, was slowly dropping from
6.1 to 5.9 mag. The enhanced activity from 20:45 UTC
onwards that is also indicated in the video numbers is
thus confirmed visually.
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