[Prev][Next][Index][Thread]
Re: (meteorobs) Clustering (a new approach?)...
There are some papers regarding "meteor clustering" listed on IMO's web
site, but unfortunately there are no link to the full texts:
http://www.imodot net/bib/metclu0.html
But I'm very pretentious and can't help suggesting two different
hypothesis to the "clustering effect".
The first hypothesis is the "meteoroid family" (meteoroids recently
originated from bigger particles). Let's make some assumptions and
analize the possibilities.
1) For the particles to break-up, they have to be heavier than average
in a given stream and fragile. These assumptions makes newly ejected
cometary substreams the best candidates for secondary break-ups (the
leonids and perseids of the last few years for example). On the other
hand, these same assumptions can exclude the Geminids stream (until
now), whose particles are more rigid (asteroidal origins) and mostly
old. But there is a non-gravitacional effect called Poynting-Robertson
that causes the smaller particles to spiral in towards the sun, hence
the bigger ones become more concentrated in the periphery of the stream.
In the case of geminids the Jupiter's gravity is distorting and pulling
the stream through Earth's orbit, so that we never pass through the same
section twice and nowadays the Earth is crossing exactly the periphery
of the stream. This can explain the high ZHR of the last decades and the
high number of bright meteors and the clustering effect observed by many
observers this year (caused by larger particles recently broken apart).
Maybe we are actually attending the reahearsals of the final act of the
geminids shower.
2) After break-up, the particles can spread out in all directions. Thus
the area in which the members of the new meteoroid family can be found
would be a sphere. We have to determine the size of this sphere taking
into account the density of the stream. The higher the density of
meteoroids, the smaller the sphere, it's a matter of statistics. The
velocity of the new particles relative to each other is not important
here, because either slow or high a relative velocity, the particles
have to be inside the sphere of probability to be considered a possible
family. The sphere will certainly be small enough that we won't have to
worry about gravitacional and non-gravitacional effects (that could
distort the sphere). How about a 70 km diameter sphere of probability (1
second for the leonids)???
3) The interaction between the sphere of probability and the Earth's
atmosphere will create some distortions. The sphere will project either
a circle or ellipses of probability in the upper levels of the
atmosphere, depending on the radiant's elevation. The lower the
elevation the larger the distortions. The different possible observer's
points of view of these projections in the upper atmosphere can cause
even greater distortions. We can reduce the problem of distortions
choosing just one section of the sky to observe. The zenith would be the
logical choice because it's where the distortions are the smallest. We
should specify both a diameter around the zenith and a time span within
which two (or more) meteors from a given stream have to show up to be
considered as a possible "family". Just the meteors sighted within this
area and time span should be reported. The time span would be less than
2 second for most showers (in my opinion).
4) The higher the magnitude of the candidates and the population index
of the stream the higher the probability of being a real "family".
Again, it's a matter of statistics.
The other hypothesis is the "micro-stream". This hypothesis would be
much easier to study. The only problem would be getting the very precise
timings required for the analysis. The "micro-streams" should stand out
as meteor clusters appeared to various observers sequentially from east
to west in a determined velocity. We can't determine the time span and
area of the sky within which the meteors have to appear because we don't
know "a priori" the width of the hypothetical "micro-streams".
Is not so difficult, I think.
Kiko Soares
P. Prudente - Brasil
22.07 S - 51.22 W
_________________________________________________________
Do You Yahoo!?
Get your free @yahoo.com address at http://mail.yahoo.com
The archive and Web site for our list is at http://www.meteorobs.org
If you are interested in complete links on the 2001 LEONIDS, see:
http://www.meteorobs.org/storms.html
To stop getting email from the 'meteorobs' list, use the Web form at:
http://www.meteorobs.org/subscribe.html
Follow-Ups:
References: