(meteorobs) ejection velocities and ejection times

[Mikhail Maslov]

Hello, Peter, Mikiya,...

BPV>   Unfortunately I deleted the postings that told us where to look, but we were recently directed to look up some 2004 Giacobinid and Leonid meteor shower timings at a website.  I did, and found
BPV> graphics of AUs from Earth at nodal crossings, timings, etc.  Below that was a presentation of perihelion passage, ejection velocities, etc.  
BPV>   My question is this:  Are these ejection velocities the velocities extant when the comet reached its nodal crossing in those years?  After all, comets are spewing a lot of material for months
BPV> before and after nodal crossings.  Wouldn't those periods need to be looked at as well?

As far as I concerned, in such a modelling of meteor trails evolution
one can assume that all particles of given trail were ejected by the
comet at the momemt of perihelion passage. Because the comet is
most active when it's near perihelion and this active period is
relatively small to the whole orbital period of the comet, one can
get acceptable accuracy with such 'one moment' ejection. So far ejection
velocities are related to this perihelion passage. And these
velocities show important features of the relative meteor outburst on
the Earth. The more is this velocity the less would be the average
brightness of meteors during outburst, because we can reasonably
assume that bigger particles can have lower ejection velocities. And
very small velocities means that activity could be relatively low
becaise amounts of large meteoriods causing bright meteors are small
comparing to other trail parts.
I don't know if this principle (one moment ejection) was used in the
predictions by Sato. But if so, Peter's latest questions lose their
sence. According to one-moment ejection principle periods before and
after nodal crossings are not considered as well as the nodal crossing
itself unless it coincides with perihelion point.


BPV>   For instance, wouldn't a high ejection velocity at one time perhaps be comparable to a lower ejection
BPV> velocity at a different period in orbit?
Certainly yes. Comet velocity at different orbit points varys very
greatly, from one to several orders. When comet moves slower, relative
ejection velocity of meteoroids will become higher and differencies
between comet and average meteoroid will be increasing. Also, high
ejection velocity near perihelion may be comparable to lower ejection
velocity at the points closer to aphelion.
Hope this helps.


About Giacobinids this year, I can say that possibility of any
outburst was very low for several reasons. The main are very old age
of the trails and relatively great miss distance of 0.002-0.003 a.e.
It would still be good for Leonids but Giacobinids trails should be
much more slim. In the past Giacobinids outbursts occured when the
Earth passed directly (at a very small distance) of relatively young
trails.
Low ejecttion velocities also lower outburst possibility (see above)
And on 'meteorobs' was mentioned that these trails for 2004 were
already affected by Jupiter and Earth, it also increases the chances
to face 'empty trails'.
According to Sato predictions, the more interesting case for
Giacobinids is in 2011. These trails are younger and much closer than
in 2004, especially trail 1894.
Also it would be very interesting to look at predictions for
Giacobinids 2018 and 2025.


About confusion with predictions. I heard about Mikiya Sato in
discussing June Bootids outburst this summer. NMS's site is mainly in
Japanese, so...
I'm sorry, but if this mistake is even a small part of reasons which
led Mikiya to 'meteorobs', I would be very glad.

Best regards, Mikhail Maslov