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(meteorobs) Radiant Rising, No. 2, June 1997
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RADIANT RISING Number 2, June 1997
New Jersey Astronomical Society North American Meteor Network
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The popularity of radio observing is evident in this issue of R/R. In
addition to the feature article sent in by Peter Jenniskens, some results of
the ALPO radio work was submitted by Harry Kelsey and Bob Lunsford. -[Mark
Davis]
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Global-MS-Net: A Global Network of Meteor Scatter Stations
by P. Jenniskens, I. Yrjola
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1. Introduction
The impact on Jupiter of comet Schoemaker-Levy 9, one fragment at a time in
July of 1994, has made a wider range of people aware of the danger of comet
and asteroid impacts on Earth. Scientists have proposed a systematic search
for near-Earth asteroids and comets using dedicated telescopes that would
hunt for the faint moving points of light in the sea of stars on the sky.
Short period asteroids and comets come back to the neighbourhood of Earth's
orbit every 4-10 years or so. Hence, it is thought to be possible to find
nearly all large objects that can come close to Earth in a period of about
25 years [1].
That does not include comets with long orbital period. Those will remain
illusive and may be discovered only when it is too late [2]. Examples of
such comets are Hale-Bopp and comet Hyakutake. Both comets do not come close
to the Earth's orbit and pose no danger to us, but others will.
We are now proposing to detect the presence of such long-period comets that can
come close to the Earth's orbit with a global network of meteor scatter
stations. Aim is to detect the dust particles in the orbit of these comets.
Visual observers can help identify the meteor streams.
2. Far-comet type meteor outbursts
Some years ago, we realised that the presence of long period comets near the
Earth's orbit can be deduced from the meteor streams they produce on Earth. In
particular, from meteor outbursts that might be caused by the dust trail of
comets that come very close to Earth's orbit.
Meteor outbursts of the Lyrid stream (from P/Thatcher with 415 year orbital
period) and the Aurigid stream (from P/Kiess with 1900 year orbital period)
were such events. Also the alpha-Monocerotids seemed to be such a stream,
although the proposed association with comet 1944 I was uncertain. The
debate on these outbursts usually assumes that a cloud of dust with a 60 or
10 year orbital period is responsible [3], because the Lyrids returned in
1803, 1922 and 1982 with a sixty year interval, and the alpha-Monocerotids
returned in 1925, 1935, and 1985, with a ten year interval. However, the
late father of meteor stream astronomy, Lubor Kresak, has argued that a
short period retrograde orbit is unlikely and a trail of dust might be
intersecting the Earth's orbit on occasion [4].
That hypothesis got support from a return of the Aurigid stream in 1994,
which did not fit into a simple sequence with the other returns of 1935 and
1986. Closer inspection revealed that the Lyrid, Aurigid and
alpha-Monocerotid streams returned when the planets Jupiter and Saturn were
at specific positions in their orbit [5]. In such a way that only two
configurations coincided with the outbursts. Either Jupiter was in direction
A and Saturn in direction B, or Jupiter was in direction B and Saturn in
direction A. In the case of the alpha-Monocerotids that was causing a
sequence with a ten year period interval followed by a fifty year period
interval. The two planetary positions both had the same effect on the Sun's
position with respect to the barycenter of the solar system. It seemed as if
the particles were moving around the wobbling Sun, while the Earth was
moving around the barycenter of the solar system.
In November of 1995, the planets would be positioned in much the same way as
during the 1935 alpha-Monocerotid outburst and we predicted that another
outburst might occur [6]. That event happened much as expected and was
observed by many observers in Europe. A dedicated effort to observe this
stream was organised by the Dutch Meteor Society in the south of Spain, with
support of the Spanish Meteor Society SOMYCE at a nearby site. During that
campaign the orbits of three alpha-Monocerotids were photographed from two
or more sites and seven alpha-Monocerotids were captured on video.
The results of that effort were recently published in the Astrophysical Journal
(April 10 issue), in a paper co-authored by Hans Betlem, Marc de Lignie and
Marco Langbroek of DMS [7]. It was found that the meteoroids had a long
period orbit, putting an end to old ideas of a 10-year period orbit and
proving the concept that a trail of dust was wagging in space, occasionally
directed towards Earth by the gravitational forces of the planets.
We were also able to get an idea of the size of the comet that should be causing
this trail of dust. It is a small one, perhaps 0.8 kilometers accross. The
orbit of the comet should be much the same as that of the dust particles
and, potentially, we could now start looking in that part of its orbit where
the comet might pose a danger to Earth.
Finding other such streams
There must be many more of such trails of dust near the Earth's orbit.
Accounts of meteor outbursts not linked to a comet are numerous. Thus far we
know of at least 14 streams that cause such outbursts. There may be at least
50 more given the number of long period comets that are expected to come to
within 0.010 AU from the Earth's orbit.
How do we find all these trails of dust? Watching the sky at all hours of
the year is a little difficult. These outbursts are brief, lasting perhaps
an hour or less. There are more than 8000 hours in a year. Even with a lot
of good visual observers only a small percentage of the time will be
covered. Still, this is our most fruitfull way at present to find such
streams and observers are requested to report any suspicious meteor activity.
The most suitable technique for finding meteor outbursts of this type is by
means of meteor scattering. Excellent work in this area has been done by
many observers. We just want to mention de Meyere and Steyaert [8], Pilon
[9], Mason [10], Lehtoranta [11], van Wassenhove [12], Manley [13], Artoos
[14], Morrow and Moore [15], Tepliczky and Spanyi [16], Kristensen [17],
Shimoda et al. [18], Suzuki and Nakamura [19], Richardson [20], White [21],
Schoenmaker and Bus [22]. But the work usually concentrates on the major
streams and little continuous monitoring is done.
Advantages of an automatic meteor counting system using meteor scatter are the
possibility to keep an eye on the level of meteor activity 24 hours a day,
including daytime. The technique needs little manpower and is not very
expensive to run. Disadvantages are that the fast showers are not so easily
detected and that no information is obtained about what shower is causing
the outburst. But once a shower has been seen in a given year, it is
possible to wait until the planet positions are similar again and go out for
a dedicated observation like during the alpha-Monocerotids.
In order to monitor all possible radiants at all times, we propose a network of
amateurs running a meteor scatter system at various places in the world, a
global meteor scatter network (Global MS Net). That allows a comparison of
data, so we can recognize interferences from true meteor activity, and from
the different responses can we give some estimate of where the radiant
should be.
We have proceeded to transplant a working meteor scatter system of Ilkka Yrjola,
from Kuusankoski, Finland, to the island of Hawaii, where Paul Sears has not
succeeded in getting automatic counts of meteor activity. Paul's first result is
the detection of the Leonid outburst of 1996 (Fig. 1). The system still needs
further improvement to limit the problems with interference, but it shows
that the concept works.
We would like to invite more amateur astronomers to implement such meteor
scatter techniques for monitoring the meteor sky at other remote sites on
Earth. The project may also give a new goal to ongoing observing efforts,
such as that of David Meisel of the American Meteor Society, who has long
championed a network of radio meteor scatter stations in the United States
and K. Suzuki and Nakamura with other Japanese observers have created an
impressive network in Japan. If anything, the Global-MS-Net project may
generate enjoyable contacts among observers interested in observing the
meteor streams. For further information see our website at:
http://prometheus.arc.nasadot gov/division/ssx/ssx_indiv_pages/pjenniskens/
Global-MS-Net/GlobalMSNet.html
References
[1] David Morrison, 1992, The Spaceguard Survey, Report of the NASA
International Near-Earth-Object Detection Workshop, JPL, 52 pp.
[2] Marsden B.G., Steel D.I. 1994, in Hazards due to Comets and Asteroids (ed.
Gehrels T.), The University of Arizona Press 221-239.
[3] Porubcan V., Stohl J., 1992, in Asteroids, Comets, Meteors 1991, A.W.
Harris, E. Bowell, eds., LPI Houston, p. 469; Rendtel J., Brown P., Molau
S., 1996, MNRAS...
[4] Kresak L., 1958, Bull Astron. Inst. Czech. 9, 88
[5] P. Jenniskens, 1996, Astron. Astrophysics 317, 953
[6] P. Jenniskens, 1995, WGN, the Journal of IMO, 23, 84
[7] P. Jenniskens, H. Betlem, M. de Lignie, M. Langbroek, 1997, Astrophysical
Journal 479, 441 (April 10)
[8] de Meyere M., Steyaert C., 1984, Werkgroepnieuws, Journal of the VVS
SEction on Meteors 12, 171
[9] Pilon K.V., 1984, Meteoros, Journal of the BMS 14,10
[10] Mason J., 1986, J. Britt. Astron. Assoc. 96, 118
[11] Lehtoranta V.K., 1987, Radiant, Journal of the DMS 9, 101
[12] van Wassenhove J., 1987, WGN, Journal of IMO 15, 116
[13] Manley T.R., 1990, WGN, Journal of IMO 18, 163
[14] Artoos D., 1990, WGN, Journal of IMO 18, 101
[15] Morrow M.J., Moore B.R., 1990, WGN, Journal of IMO 18, 90
[16] Tepliczky I., Spanyi P., 1991, WGN, Journal of IMO 19, 216
[17] Kristensen G.M., 1991, WGN, Journal of IMO 19, 206
[18] Shimoda C., Suzuki K., Maeda K., 1993, WGN, Journal of IMO 21, 130
[19] Suzuki K., Nakamura T., 1995, WGN, Journal of iMO 23, 17
[20] Richardson J., 1995, WGN, Journal of IMO 23, 56
[21] White R., 1995, WGN, Journal of IMO 23, 62
[22] Bus E.P., 1995, Radiant, Journal of the DMS 17, 43
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A.L.P.O. METEOR FORWARD SCATTER RADIO OBSERVATIONS
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Enhancement Duration Scale Signal Strength (SS)
B-Dense - 0.5 to 3.0 seconds Lo Med Hi
C-Dense - 0.5 second or less Tropospherics (INT)
X-Dense - 3.0 seconds or more Lo Med Hi
Sporadic E = Es
Radio Freq Int = RFI
NOTE: Each observation hour is recorded in three 20 minute segments. The Antenna
Heading is NE (45o). Observing Frequency is 89.7 MHz. Observer: Harry W. Kelsey
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UT
Date
APR 97 Hr-UT X-Dense B-Dense C-Dense SS INT Total
4-1 14-15 2-1-5 1-4-5 Hi None 18
4-1 15-16 3-3-0 3-3-2 Med " 14
4-2a? 14-15 2-2-0 5-4-4 5-5-6 Med " 33
4-2 1520-1620 0-1-0 6-2-3 4-4-6 Med " 26
4-3a 14-15 4-6-4 6-8-6 Med " 34
4-4 14-15 4-7-8 4-4-0 Med " 27
4-4a 17-18 2-8-4 5-7-5 Med " 31
4-5 14-15 No data recorded due to antenna problem.
4-5a 17-18 2-0-1 4-3-2 4-6-8 Hi " 30
4-6 14-15 0-3-4 2-1-1 Hi " 11
4-7 14-15 0-1-0 1-4-3 3-5-9 Med " 26
4-8 14-15 4-2-3 4-3-4 Hi " 20
4-9 14-15 0-1-1 5-3-4 4-5-7 Med " 30
4-10 14-15 1-2-3 1-1-0 Hi Med-T 8
4-11 No data recorded because of operator error.
4-12 14-15 0-0-2 2-1-1 5-7-2 Hi None 20
4-13 14-15 3-0-4 1-2-2 Hi " 12
4-14 14-15 2-0-0 3-1-2 2-6-4 Hi Lo-T 20
4-15 14-15 1-2-2 5-3-2 5-1-5 Hi None 26
4-16 14-15 2-0-0 0-5-3 2-4-6 Hi " 22
4-17b 14-15 0-1-1 4-2-6 7-12-6 Med+ " 39
4-18b 14-15 4-2-5 6-4-2 Hi Lo-T 23
4-19c 14-15 0-3-1 7-9-6 4-4-5 Hi None 39
4-20c 14-15 0-1-1 3-1-5 4-4-4 Hi RFI- 23
4-20d 1630-1730 2-1-3 7-5-7 7-8-7 Med- None 47
4-20d 2230-2330 0-1-1 5-2-3 5-9-2 Med+ None 28
4-21c 14-15 2-2-4 5-2-1 7-7-7 Hi None 38
4-21d 1630-1730 *1-2-2 11-9-6 9-5-13 Med+ None 58
*1=26 second duration
4-22c 14-15 3-1-2 10-6-5 7-8-6 Hi None 48
4-23 14-15 0-1-0 6-2-4 4-8-3 Hi None 28
4-24c 14-15 2-1-0 5-6-6 4-9-6 Hi None 39
4-25c 14-15 0-1-2 3-5-4 5-4-5 Hi None 29
4-26 14-15 4-0-9 4-5-6 Med+ None 28
4-26d 1630-1730 2-0-0 6-6-6 8-8-7 Med None 43
4-27 14-15 1-1-1 4-3-2 3-3-9 Hi- Lo-T 27
4-27d 1630-1730 3-3-0 9-4-5 4-6-3 Lo+ Lo-T 37
4-28 No Data Because of medical intervention.
4-29 14-15 3-3-4 2-5-4 Med Lo-T 21
4-30 14-15 2-1-1 6-4-8 2-4-6 Hi- None 34
4-30d 16-17 1-1-1 5-2-4 8-3-5 Med RFI 30
a Tau Draconids
b Librids
c Lyrids
d April Piscids (Daylight)
Commentary, Apr 1 through Apr 8: Of the two X events recorded Apr 2 at 1400
UT in the first 20 minute segment, the first persisted for 12 seconds and the
second for 11 seconds.
April 9 through April 16: This period was marked by moderate activity with
notable occurences on only three dates. On April 9 a major solar disturbance
occured that may or may not have contributed to a slight increase in
recorded meteor reflectance.
April 17 through April 24: The April Piscids, a predicted daylight shower, was
investigated in the east and west 60-30 zones and found to be more
productive in the east zone at 1630 UT. There was also apparent Librid and
Lyrid activity
recorded in the west 60-30 zone at 1400 UT.
April 25 through April 30: The daylight April Piscids activity was apparent in
the east 60-30 zone. Their count on April 30 would probably have increased
if the RFI hadn't occured throughout the second segment.
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NAMN NEWS and NOTES
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Each issue of R/R will contain information related to the North American
Meteor Network in this section. This issue features the member profile of
James Riggs. -[Mark Davis]
Name: James Willborn Riggs, Jr.
Born: 15 March 1914
Location: Houston, Texas. Raised in Baytown, TX.
Education: Four years of undergraduate studies at University of Texas. Spent
five years at Texas A&M University for graduate studies in physics.
Occupation: Labor in Bayton Exxon refinery. Door to door book saleman. Navy
medical corpman. High school teacher. Finally settled in Riverside, CA.
where I spent 39 years as a teacher of physics at Las Sierra University.
Been retired since 1986. Have forgotten all the physics, so I am a student
again under the guidance of Jim Richardson, David Meisel, Dave Holman, Bob
Lunsford and all the NAMN crew!
Astronomy: Much of astronomy is related to physics so I was naturally
attracted to radio meteor observation during my retirement years. My first
efforts in radio meteor observation was monitoring an aircraft beacon about
30 miles from my home in West Point, CA area. I was not getting the normal
diurnal meteor profiles so this effort turned out to be just a time of
learning. Through some one I learned about METEOR NEWS from which I read
about Jim Richardson's radiometeor system. A contact with Dr. David Meisel
of AMS yielded a construction manual for the system. One year and a half
later I have one and getting good meteor profiles. I am interested in meteor
photohgraphy with a rotation shutter. In the future I hope to get into the
use of video to record meteors.
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Copyright 1997 New Jersey Astronomical Society & North American Meteor Network