Publ. Natl. Astron. Obs. Japan Vol. 12. 11 – 80 (2009)

Fireball Monitoring Observation at the Kiso Observatory
Akihiko MIYASHITA, Kyoko TANAKA, Hiroshi WATANABE, Hiroyoshi TANABE,Mikiya SATO and Jun-ichi WATANABE(Received 2008 October 25; Accepted 2009 Jannary 30)
Abstract
Sequential photographic monitor of fireballs was carried out with using an all-sky camera during the period
between 1977 and 1990 at Kiso Observatory. Total number of observed fireballs is 742 and their apparent magnitude is brighter than +1 in average. The obtained data are valuable for investigating the annual variation of thenumber of the fireballs and for unexpected display of the meteor showers in this period. In this paper, we present
the detailed data of all the fireballs detected with our system and their images as archival data. Some results of thestatistical studies are also presented.
Key words: monitoring observation, fireballs, meteors, meteoroids, all sky camera, Kiso Observatory

1. Introduction
Monitoring observations of fireballs are important in
two astronomical aspects. One is for estimating the influx
rate of the fireball-class meteoroids into the Earth’s atmosphere. This can be useful to the NEA monitoring program
recommended by the IAU (Chapman 2008). In order to estimate the probability of impact hazard by the NEA objects,
we should know the precise mass distribution of the NEAs,
including fireball-class objects. However, the size of suchobjects is too small to be observed by ground-based telescopes used for the NEA monitoring programs in general.
Hence the estimate of the influx rate of such objects should
be done by such fireball monitoring observation. The otheraspect is to determine the population index of the fireballs.
This index is related to the mass index of the fireball-classmeteoroids in the space near the Earth’s orbit. The discontinuity of the mass index has been pointed out around themass of fireball-class meteoroids (Chapman 2008). Becauseof its low flux rate, we cannot carry out any in-situ measurement by artificial satellites. It is appropriate to perform longterm monitoring observations under a uniform condition for
determining the mass influx rate of such meteoroids.
An automatic all-sky camera has been operated at theKiso Observatory since 1977. Although the main purpose ofthis camera is to monitor the weather condition during theautomatic airglow observation by photoelectric zenith photometer (Tanabe et al. 1992; Atlas of Zenith Airglow,
National Astr. Obs.,1989), this camera system can be used tomonitor fireballs and bright meteors. The aim of this paper isto present all the data of detected fireballs, which could not

be included in the paper presented in 1993 (Miyashita et al.
1993), during our operation period (1977-1990) as anarchive for future investigations, along with the results of thebasic statistics of the fireballs detected by this all-sky camera
at Kiso Observatory.

2. Observation and Data Reduction
The all-sky camera was installed in 1977 at the Kiso
Observatory, Institute of Astronomy, University of Tokyo.
The location is λ=137°37’39” (9h10m30.8s), ψ=+35°47’38.7”, and 1130m above sea level. Figure 1 shows theschematic diagram of the camera system, which is operated
automatically every night. The camera was set in the observation building to protect from rain. The monitoring observation is performed through the protecting glass, which wascoated by transparent conducting of the In2O3 in order towarm it up electrically. This device protects the glass(Miyashita et al.1979), and is useful for avoiding dew. The
cover upon the glass is operated by a daylight switch. The
system consists of 35mm camera (type Nikon F) with a fisheye lens ( type Nikkor F/8) with a focal length f=16 mm
between 1977 and 1980. After March 1980, another type offish-eye lens with a focal length f=8mm ( F/2.8 ) was used.
The Fuji SSS (Neopan ASA-400) film with 100 feet length,
which provides 750 frames, is used along with the motordrive system. The film is developed by Fuji Pandol at thetemperature 20°C with 15min. This camera is set to takeone-hour exposure per frame. The maximum period of theautomatic monitoring is about one month, which is limitedby the length of the photographic film.
We checked all the frames taken by all-sky camera by12Akihiko MIYASHITA and others

eye-inspection, and recorded the positions and the maximum
apparent brightness of the meteor trails. The apparent magnitudes were estimated by comparing the trails to known stars.
The positions of the beginning and ending points were measured by overlaying the transparent measure for the altazimuth coordinates diagram. We inspected the star trails oneach frame to determine if the frame can be used for themonitoring observation. All frames were divided into threeclasses (weight 1, 0.5, 0) according to the observational con-ditions. The clear condition (weight 1) is calculated in100%,the cirrus or partly cloudy (weight 0.5) is in 50% and cloudy(weight 0) is in 0%. Adding the weight, we can roughly estimate the total observation time in unit of hour.
During 1977-1990, we obtained 32254 frames in total,
and 8900 frames of them could be used to monitor fireballs.
Total number of fireballs observed was 742 during the effective observation time of 8900 hours.

Figure 1. Schematic diagram of the all-sky camera system at the Kiso Observatory

Figure 4. Glass cover coated of the In2O3

Figure 2. Camera with fish-eye lensFigure 3. Cover operated automatic

3. Magnitude Calibration
There is a systematic difference between the apparent
magnitude of fireballs and the estimated their true magnitude, because of the rapid angular speed and the reciprocallow failure in emulsion. In order to estimate this difference
quantitatively, we performed an experiment. The camera wasset horizontally on a turn table, and was exposed in the rotation with an appropriate angular speed (22.5°/sec). Suchframe contains many trails of bright planets, of which magnitudes are known. Comparing such experimental trail
images with the apparent trails in a sidereal speed on the nor-Fireball Monitoring Observation at the Kiso Observatory

mal frames, we obtained approximate value of the systematic
magnitudes difference as -7.0. This magnitude difference isfor the G-type stars, and needs adjustments for color difference. Because we used the panchromatic emulsion for thisobservation, the color index derived by Ceplecha (1959) wasused in this study. Because of the lack of the information,
we assumed the constant index of -2.0 for the fireballs of
which photographic magnitude is brighter than +2. This
assumption may be supported by the result of Davis’s photoelectric study (1959). The applied index correction is shownin table 1. Because the limiting apparent magnitude of stars
in this camera is about 5, the average threshold of sensitivityof this monitoring observation is approximately +1 in thevisual magnitude.

4. Results
All data obtained for each fireball is listed in table 2. It
contains date and time, exposure time, the altitude andazimuth information of both starting and ending points ofeach fireball trail. The direction of the trail was judged fromthe brightness variation of the trail. It also contains thelength of the trails and the apparent magnitude together withthe estimated magnitude in the basis of table 1. Using thedirection of each trail, we also judged if it belonged toknown meteor showers or not. Special comments were also
added if they were appropriate. The images of the fireballs
are mainly processed for appropriate trimming in order toshow them clearly. We did not list the images of faint fireballs in this image archive.
Using the corrected magnitude data, we can obtain thepopulation index r, which indicates the increase of numberof fireballs from a magnitude class m to m+1 as N (m+1)= r N ( m ). Figure 5 shows the cumulative distribution of
the magnitude of fireballs detected in our system. The population index of 1.4 ± 0.3 is derived from the fireballs of
which magnitude ranges between 2 and -4. This value iscomparable with the value of 1.2 to 1.9 derived by Sanchez
and Gonzalez (2004). The overall feature of the seasonalvariation is consistent with the result obtained by Sanchez
and Gonzalez (2004).
Figure 6 shows the seasonal variation of the number ofthe detected fireballs. The effect of the rainy season in Japanaround June and July is clearly shown, and corresponding tothis period the actual number of fireballs recorded is small in
the figure, while the estimated number after the weather factor correction is not small. The local maxima both in August

13and November are clearly shown, possibly due to thePerseids and Taurids, respectively.
Inspecting the detected fireballs, we noticed the fivecases of the enhancement of fireballs, which may be related
to the possible unusual activities of the meteor showers;
Lyrids on April 22 in 1980, Ursides on December 22 in1981, Virginids on April 15 in 1982, Taurids on November
in 1988, and Geminids on 14 December in 1988. There are
two possibilities for the cases. One is the enhancements of
only bright or fireball-class meteors such like the Leonids
storm in 1998(Asher et al. 1999). Another is the enhancements occurred over the wide mass range of meteoroids. We
do not have enough information to discriminate these twocases for our detected activities. It is definitely the evidence
that such all-sky camera is valuable for monitoring the activities of meteor showers, and the detailed investigation can bedone by using our archive in the future.
We are grateful to all the staff in the Kiso Observatory
for their cooperative efforts to maintain the automatic observation system.

Figure 5. Cumulative distrbution of the visual magnitude

Figure 6. Seasonal variation of the ovserved fireballs. The marks ofcircle are number of Observed fireballs. The marks ofsquare are corrected number by the weather factor. Themarks of lozenge are weather factor (%)

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Akihiko MIYASHITA and othersTable 1. Correction between photographic and visual magnitude

REFERENCES
Asher, D.J., Bailey, M.E, Emel’Yanenko, V.V., 1999,
Monthly Notices of the Royal Astronomical Society, 304,
L53.
Ceplecha, Z., 1959, Bull. Astron.Inst.Czechosl., 10, 39
Chapman, C.R., 2008, Earth, Moon and Planets, 102, 417
Davis, J., 1963, Smith.Contrib.Astrophys., 7, 233.
Miyashita, A., Tanaka, K., Watanabe, H., Watanabe, J.,
1993, In Meteoroids and their parent bodies, Proceedingsof the International Astronomical Symposium held at

Smolenice, Slovakia, July 6–12, 1992, Bratislava:
Astronomical Institute, Slovak Academy of Sciences,edited by J. Stohl and I.P. Williams, p.319
Miyashita, A., Katsube, Y., and Katsube, S., 1979, Tokyo
Astronomical Observatory Report, 18, 593 (in Japanese).
Snachez, O.B., Gonzalez, F.O., 2004, WGN, Journal of theIMO, 32, 29
Tanabe, H., Takechi, A., Miyashita, A., and Tanaka, K.
1992, Report of the National Astronomical Observatoryof Japan, 1, 309 (in Japanese).

Fireball Monitoring Observation at the Kiso Observatory
Table 2. List of fireballs detected in our monitor

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Figure 7. Fireball Images [#1]

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Figure 8. Fireball Images [#2]

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Figure 9. Fireball Images [#3]

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Figure 10. Fireball Images [#4]

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Figure 11. Fireball Images [#5]

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Figure 12. Fireball Images [#6]

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Figure 13. Fireball Images [#7]

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Figure 14. Fireball Images [#8]

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Figure 15. Fireball Images [#9]Fireball Monitoring Observation at the Kiso Observatory

Figure 16. Fireball Images [#10]

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Figure 17. Fireball Images [#11]

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Figure 18. Fireball Images [#12]

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Figure 19. Fireball Images [#13]

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Figure 20. Fireball Images [#14]

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Figure 21. Fireball Images [#15]

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Figure 22. Fireball Images [#16]

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Figure 23. Fireball Images [#17]

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Figure 24. Fireball Images [#18]

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Figure 25. Fireball Images [#19]

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Figure 26. Fireball Images [#20]

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Figure 27. Fireball Images [#21]Fireball Monitoring Observation at the Kiso Observatory

Figure 28. Fireball Images [#22]

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Figure 29. Fireball Images [#23]

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Figure 30. Fireball Images [#24]

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Figure 31. Fireball Images [#25]

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Figure 32. Fireball Images [#26]

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Figure 33. Fireball Images [#27]

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Figure 34. Fireball Images [#28]

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Figure 35. Fireball Images [#29]

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Figure 36. Fireball Images [#30]

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Figure 37. Fireball Images [#31]

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Figure 38. Fireball Images [#32]

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Figure 39. Fireball Images [#33]

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Figure 40. Fireball Images [#34]

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Figure 41. Fireball Images [#35]

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Figure 42. Fireball Images [#36]

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Figure 43. Fireball Images [#37]

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Figure 44. Fireball Images [#38]

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Figure 45. Fireball Images [#39]

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Figure 46. Fireball Images [#40]

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Figure 47. Fireball Images [#41]

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Figure 48. Fireball Images [#42]

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Figure 49. Fireball Images [#43]

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Figure 50. Fireball Images [#44]

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Figure 51. Fireball Images [#45]

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Figure 52. Fireball Images [#46]

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Figure 53. Fireball Images [#47]

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Figure 54. Fireball Images [#48]

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Figure 55. Fireball Images [#49]

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Figure 56. Fireball Images [#50]

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Figure 57. Fireball Images [#51]

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Figure 58. Fireball Images [#52]

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Figure 59. Fireball Images [#53]

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Figure 60. Fireball Images [#54]

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Figure 61. Fireball Images [#55]