(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.


More information about the Meteorobs mailing list