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Re: (meteorobs) Leonid "radiant glow" (long)
Hi Robert,
You made a very fine contribution to the subject of "Radiant glow"!
A team of the Dutch Meteor Society (Marco Langbroek, Koen Miskotte, Robert
Haas and myself) perhaps observed such a radiant glow during the Perseid
outburst in 1993 from southern France. Another observer (Jacob Kuiper)
might have seen the same phenomenon about 600 kilometers north of our site
and exactly at the same spot on the sky. So any "earth-bound" should be
ruled out.
But regretable other well-known observers in Europe did not noticed this
very weak phenomenon. So we still are not completely sure this object is
caused by the Perseid radiant glow.
In fact we now should have much more chance to observe such a radiant glow
while the number of particles hopefully will be much more.
Did you publish your contribution somewhere on the web? If so please tell
us the URL where we can find it. I would be pleased to have a link to this
information from our DMS website. If you did not publish your analyses
somewhere on the web we would be gratefull to publish it at our website.
URL: http://home.wxsdot nl/~dms-web/
We invite you to have a look on our website for information on the Leonids
and especially the Sino-Dutch Leonid Expedition 1998. The expedition
incorporation 17 members will head to China on saturday november 7. We will
perform visual, radio, video and multistation photographic observations by
four teams at two different locations in China. All observations are
carried out in co-operation with our counterpart of the Chinese Academy of
Sciences.
Thanks again for your fine contribution on the Radiant glow of the Leonids!
We will be sure to have your documentation at hand in China!
Best wishes and clear skies!
Casper.
At 00:16 1998-11-03 +1100, you wrote:
>Observing the Leonid stream in Interplanetary space.
>
>[SUMMARY: The glow from the particles in the Leonid orbit may be
>observed around the time of the nodal crossing (1998 Nov 17.8 UT)
>at around
> R.A.(2000)Dec.
> 10h 54m +25.6d near 54 Leo
> 22h 08m -30.2d between tau PsA and lambda PsA
>
>At peak intensity it is unlikely to be obvious.]
>
>After a cursory check on the web for information on the "radiant glow"
>from the Leonids and finding nothing (see Postscript), I have made some
>calculations myself.
>
>The radiant glow may have been reported in previous meteor storms, but
>I am unaware of adequate evidence to demonstrate this conclusively.
>As I understand it, photographs in 1966 failed to show it and the region
>appears on some published photographs. However, better instruments and
>emulsions and CCDs brought to the task this year may give success.
>
>The radiant glow I am referring to is the reflection of light off the
>Leonid particles in space. Around the direction of the *true* radiant,
>and close to the time of crossing the plane of the orbit, we are looking
>along the sheet of particles within the orbit. This geometry
>concentrates the Sun's reflection from the dust. Note that the direction
>is the *true* radiant. This is from the tangent to the orbit at the node,
>which is the same direction as the velocity vector of the Leonid
>particles. It is not the direction of the *apparent* radiant which
>includes the motion of the Earth to produce the meteors we see. (A good
>analogy would be a thin column of rain falling straight down. You see
>the greatest thickness of raindrops standing under it and looking up,
>or down. In a car driving through it, the rain hits the front
>windshield, not the back, as the car's motion is added to the motion of
>raindrops. This give an "apparant radiant" for the rain in front of and
>above the car. The "true radiant" of the rain is directly up.)
>
>The direction of the *true* radiant and anti-radiant for the Leonid
>stream on 1998 Nov 17.8 UT are:
>
> R.A.(1950)Dec.
> radiant 10h 30m +28 (direction particles come from)
> anti-radiant 22h 30m -28 (direction particles go towards)
>
>However this doesn't necessarily correspond to the region of greatest
>intensity, especially as the main region of the Leonid swarm is passing
>inside the Earth's orbit. I calculated an approximate surface brightness
>as follows:
>
>1) Define the path of the orbit in the sky (line of variation) at the
> time of crossing the comet's orbital plane using the orbit of
> 55P/Tempel-Tuttle of epoch 1998 March 8.
>2) Determine the brightness of an arbitrary "standard" particle for
> various points around the orbit, correcting for the distance from the
> Sun and Earth.
>3) Assume the thickness and flux density of the stream is constant
> over a few months either side of the region we encounter this year.
>4) Determine the surface area presented to the Earth at each point in the
> orbit, for a standard unit of the stream (+/- 1 day arc from that
>point)
>5) Calculate the intensity per unit surface area (in arbitrary units).
>
>An assumption involved in 2) is that the particle brightness can be
>represented by the standard asteroid brightness formula. This is not
>true and may affect the results slightly, but the surface brightness
>varies rapidly over a short arc suggesting the fine detail is correct.
>Another assumption in 3) that the thickness of the stream is constant
>will be a reasonable approximation, but the stream will be slightly
>narrower towards perihelion. This is unlikely to affect the results,
>as the predicted brightest point of the approaching stream is,
>coincidently, very close to perihelion.
>
>Using a two day arc of the orbit gives a common number of particles
>for each calculated mid point. The apparent angular thickness of the
>stream at this point is inversely proportional to the geocentric distance.
>The apparent angular length of this two day arc of the orbit gives the
>other dimension to calculate an arbitrary surface area. The intensity
>(on an arbitrary scale) is determined by the standard asteroid formula
>for the mid point for an arbitrary "standard" particle. Note that as the
>orbit approaches the Earth, the "two-day arc" becomes grossly non-linear
>and the initial point in each table will have the surface intensity
>slightly underestimated.
>
>The Surface Intensity only applies to the time of maximum brightness and
>this will presumably occur at the peak of the shower. Thus, at the
>two times given below the surface intensity is likely to be less than at
>Nov 18.8 UT. However, the positions for the two times will give an
>indication of the motion of the glow over the course of a day.
>
>RESULTS
>
>Near the TRUE RADIANT
> 1998 November 17.3 1998 November 18.3
> (1950) Surface (1950) Surface
> R.A. Dec. Intensity R.A. Dec. Intensity
> h m o ' h m o '
>10 54.1 +23 14 28 11 47.3 +24 19 3
>10 47.7 +25 12 167 10 59.1 +26 44 59
>10 48.5 +25 32 216 ~perihelion 10 54.2 +26 38 314 ~perihelion
>10 51.2 +25 26 115 10 54.8 +26 18 169
>10 54.5 +25 11 89 10 57.0 +25 54 111
>10 58.1 +24 52 75 11 00.0 +25 27 83
>11 01.8 +24 29 65 11 03.4 +25 00 76
>11 05.6 +24 04 63 11 06.9 +24 32 64
>11 09.4 +23 39 56 11 10.5 +24 04 59
>11 13.1 +23 13 53 11 14.1 +23 35 55
>
>11 26.1 +21 36 48 11 26.8 +21 53 50
>11 36.8 +20 10 44 11 37.4 +20 23 46
>11 46.5 +18 49 41 11 47.0 +19 00 40
>11 55.1 +17 33 37 11 55.7 +17 42 38
>12 02.9 +16 23 34 12 03.6 +16 30 36
>12 09.8 +15 18 32 12 10.4 +15 24 34
>
>Near the TRUE ANTI-RADIANT
> 1998 November 17.3 1998 November 18.3
> (1950) Surface (1950) Surface
> R.A. Dec. Intensity R.A. Dec. Intensity
> h m o ' h m o '
>21 18.4 -39 33 4 21 50.3 -29 23 32
>22 04.4 -32 15 25 22 04.0 -29 28 156
>22 07.1 -31 19 216 22 05.2 -29 45 366
>22 05.4 -31 09 212 22 03.5 -30 04 156
>22 02.5 -31 14 135 22 00.7 -30 24 110
>21 59.0 -31 25 104 21 57.4 -30 44 93
>21 55.3 -31 38 86 21 53.9 -31 04 77
>21 51.5 -31 52 78 21 50.2 -31 22 73
>21 47.6 -32 07 70 21 46.4 -31 40 66
>21 43.7 -32 21 65 21 42.6 -31 57 64
>21 39.9 -32 35 63 21 38.9 -32 14 60
>21 36.1 -32 49 57 21 35.2 -32 29 55
>21 32.3 -33 02 57 21 30.3 -32 48 53
>
>21 18.2 -33 49 46 21 17.6 -33 34 49
>21 07.3 -34 21 42 21 06.9 -34 08 42
>20 57.3 -34 47 40 20 57.1 -34 35 37
>20 48.2 -35 08 39 20 48.1 -34 57 35
>20 39.7 -35 25 35 20 39.7 -35 15 35
>
>My apologies for use of 1950 coordinates. I did these calculations for
>the U.K. Schmidt Telescope, which still uses 1950 for the input
>field centres.
>
>POSTSCRIPT
>Subsequent to writing this, I came across the web page of a Japanese
>research group who are trying to observe the "Leonid Meteoric Cloud" with
>a wide field CCD camera. The main page is at
>
>http://komadori.planet.kobe-u.ac.jp/~fujii/leonid.htm
>
>and a map of the northern cloud is at
>
>http://komadori.planet.kobe-u.ac.jp/~fujii/location.htm
>
>Although it is not stated in the (english) text, the diagram does indicate
>the contraction of the stream towards perihelion. The main page also has
>excellent animations of the Earth's passage through the stream, looking
>towards both Leo and PsA. There is no indication of relative surface
>brightness in these pages however.
>
>Robert H. McNaught
>rmn@aaocbn.aaodot gov.au
>
>
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