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. 11, 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 SAO 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 one 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 C. ter Kuile from the DMS with an intensified 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 indicated in the video numbers is thus confirmed visually. ================================================================= This 'paper' was sent to or advertised on various mailing lists on Aug. 17, 2004; only a handful of typos have been corrected since. Addendum: a little poem I wrote about peak night was published in http://tech.groups.yahoo.com/group/imo-news/message/1507 - and http://www.astro.uni-bonn.de/~dfischer/skyreports/rom04/persedip.jpg takes you to my proof of having been there ...