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Re: (meteorobs) Geminids from China (Dec. 14/15 ZHUJI)

Kim,

>      Let me guess, Jin, that many of these meteors you are describing were at or
> near the horizon...?  My (limited) understanding
> is that (a) a meteor can never have too short a trail to be associated with its
> shower (but can be too long) and  (b) a meteor moving from overhead down to the
> horizon will appear to slow (and dim) somewhat near the horizon.  I had exactly
> the same experience during the Geminids.  I saw MANY meteors with short path
> lengths near the horizon moving at, say, a speed of two (slow) but I knew that
> most likely they were Geminids because they were traceable back to the radiant
> and  the Geminids were at near-peak intensity. So given your other descriptions, I
> would say it's safe to assume that many of your sporadics were Geminids.  It would
> be good to have an experienced observer give us both his/her slant on this.

For my understanding from books and postings here, the two points are like:

(a) a meteor should always be very short (trail) when it is very near its
radiant. Its trail will appear longer when it is far from the radiant.
And it should be very long when it is seen very far from the radiant.

(b) a meteor appears slower when it is observed near the radiant, but faster
when far from the radiant.

So a meteor far from radiant (say, more than 100 degrees far) should always
be long in trail and not slower (than its average speed). (theoratically)

However, I did note from my observation that meteors near horizon appear
to be short ones, except those extremely long ones with almost horizontal
motion. They were only small part of such horizontal ones in my Geminids
observation this year for my f.o.v. was almost the zenith. However, I did
note many bright meteors near the west horizon with slow and short trails,
'like water drops' when I observed the Leonids last year during the first
maximum. I included them as LEOs at the ealier part of my observation but
then I remembered the above theory and later assigned them to SPOs. They
did appear at least coinciding in time with the Leonids maximum. I finally
supposed (not in my report where all non-LEOs were SPOs) that they might
be some unusual NTA outburst during the LEO maximum - the Leonids
radiant was low at east at that time, and TAU was about in middle of
LEO and my west horizon... Except my previous comment that there might be
some non-GEMs including in GEM reports, I also felt that there were
some NTAs were regarded as LEOs in previous Leonids reports (I mean those
received by IMO).

Anyway, I myself is also a new observer and I still need more observations
to understand all those things together with other observers.

With best regards, Jin

========================================================================
Jin Zhu                           | Tel.: +86-10-62759888, 62756612 (O)
Beijing Astronomical Observatory  |       +86-10-62579689 (H)
Chinese Academy of Sciences       |       +86-314-5054767 (Schmidt dome)
P. R. China                       | Fax : +86-10-62765031 or 64888731
------------------------------------------------------------------------
email: zj@bac.pkudot edu.cn or jinzhu@sun.ihep.ac.cn
WWW Home Page: http://vega.bac.pkudot edu.cn/~zj
Pager: zhu_jin@263dot net (only Sub. line) OR +86-10-64256688 PIN 82333
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