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Re: (meteorobs) Trains in dim, fast meteors?
In a message dated 96-11-19 10:51:26 EST, you write:
<< Another unusual (albeit quiet) event this weekend was that I noted in my
log a
4.5 magnitude Leonid with a long wake! (I.e., a train somewhere just below
0.5
seconds.) Being aware of the 3rd magnitude rule-of-thumb "cutoff" for meteor
trains, I was very surprised by this! The train actually appeared nearly as
bright as the meteor, and left a very clear impression.<<
For the Leonids I find this actually normal...that is to see 3rd and even 4th
mag Leonids producing trains. I recorded two +3 Leonids leaving 1 and a2
second trains and a +4 leaving a 1 second train as well on the 17th.
>>What exactly is the reasoning behind the 3rd magnitude cutoff? Is it
because of
the difficulty of detecting fainter ephemeral extended objects with the eye?
Or
are there actual physical explanations that make smaller material in a
stream
(i.e., meteoroids resulting in dimmer meteors) unlikely to produce trains?<<
I believe all meteors produce trains. Most normal trains are ionized air I
believe? the more of this air ionized, the easier it will be seen. Small
particles have only so much energy to which they can ionize the air...Faster
the particles also that more energy. Somewhere there is a cap. For most
people near +3 and sometimes +4 is the limit that their eyes will see any
ionization for very fast meteors. If the meteors are quite a bit
slower...let's say like that of the Taurids. The same sized particles don't
have the same amount of stored energy due to their slower velocities. Thus
less ionization to be seen. Also no doubt one's individual LM will help
determine to what extent they will be able to perceive faint trains.
Individuals with LM's near +7 I would expect more trains from +3's and +4's
to be seen. On my best viewing nites, my normal LM is around 6.0. For
others perhaps near +6.5 is their normal LM. I suspect that this range
probably covers a large percentage of observers and their abilities to see
trains limits most folks to about the same magnitude meteors. Perhaps that's
why +3 mag meteors is the general rule of thumb...but not chiseled in stone.
>>If its the former, then significant variations in individual perception
and in
observing-site transparency would certainly come into play. If the latter,
then
wouldn't geocentric velocity (e.g., 72 km/s) also be a factor in determining
how
small a particle would result in a train. Just curious,<<
Lew<<
Yes....Just about everyone's train percentages based on shower speeds shows
strongly this velocity relationship to train production.
BTW...my % of trains for the Leonids on the 17th came to 69%. Last year I
had 62%. No doubt I saw a higher percentage of briter than dimmer Leonids
this year than in the past. And this should reflect in an increase of train
percentages. From all the meteor reports that I've been reading lately about
people seeing a lot more brite Leonids and in some cases relatively few
dimmer ones, I suspect that this will show an increase in Leonid train
percentages from their previous years.
George Z.