(meteorobs) Meteor nomenclature, trail, train etc!

Ed Majden epmajden at shaw.ca
Sat Aug 27 18:47:55 EDT 2005



Subject:  Meteor nomenclature, trail, train etc!

Re-post without attachments!


Subject: Meteor nomenclature, trail, train etc!

    Someone asked the differences between, trail, train, and path etc
regarding meteors.  I asked the same or similar question of Dr. Jiri
Borovicka in 2000 and his reply is included below.  If enough people adopt
Jiri's et al definitions, I expect the IAU will eventually accept them as
the standard.  This is important, so when discussions take place, everyone
is talking about the same thing.
Hope this helps!

Ed Majden  B.C. - Fireball Network Coordinator - AMS Meteor Spectroscopy
West Coast Sandia Bolide Detection Station
Courtenay B.C. CANADA

http://members.shaw.ca/epmajden/index.htm




From: "Jiri Borovicka"
Date: Thu, 03 Feb 2000 13:05:22 +0100
To: "Ed Majden" 

Dear Ed

the nomenclature of all the interesting objects, which could
perhaps generally be called "meteor afterglows", is not firmly fixed.
To my understanding, the terms "trail" and "train" are sometimes
used as synonyms. The "train" is used more often, especially
for persistent long-duration trains. The problem is that the physical
nature of all these objects is not well understood yet, so the
classification is rather descriptive. Nevertheless, I try to give
a consistent classification below, which follows the traditional
terminology used in meteor literature (from Millman, Halliday etc.)
and takes into account the present understanding of the objects:

1. METEOR WAKE

A luminosity just behind the meteor. It moves with the meteor
and forms a kind of tail. The wake is often present in bright
fireballs, which are then sometimes described as a comet-like objects
by the witnesses. In this sense, the meteor can be described as
consisting of meteor head and meteor wake. At a given position,
the wake duration is only a fraction of second.

The spectrum of meteor wake is different from the spectrum of meteor
head. The wake spectrum consists chiefly from low excitation lines.
Typical lines belong to Na I, Fe I, Mg I, Ca I, i.e. to the atoms
released from the meteoroid.

After a meteoroid fragmentation, small fragments decelerate more
rapidly and stay behind the main body. They may look like a wake of the
main body but this is not a true head+wake, rather a multiple meteor
with similar spectra in all parts.

2. SHORT-DURATION METEOR TRAINS (OR TRAILS)

Luminous trains left behind the meteor for up to about 3 seconds.
They are often observed visually and by video techniques in fast
meteors like Perseids. They are present also in faint meteors, of
magnitude +4 or so. In fact the ratio of the train/meteor brightness is
larger in faint meteors than in bright meteors. The train is not
connected with the meteor. In fact, it forms at a given position
with some delay after the meteor passage. The the train is also
considerably shifted to higher altitudes than the meteor which produced
it.

The short-duration trains are formed by only one spectral line,
the green auroral lines of neutral atomic oxygen at 5577 A. This
is a forbidden line. The luminosity is produced (very probably) by
the atmospheric oxygen.

3. PERSISTENT LONG-DURATION METEOR TRAINS

Luminous trains left behind the meteor for from 3 seconds up to
more than an hour in rare cases. The trains are self-luminous, i.e.
the luminosity is not produced by reflected sunlight or other external
source. Persistent trains are produced much more easily by fast
meteors. Leonids are very favorable. The typical altitude for train
formation is 90 km. Persistent trains are affected by high altitude
winds and  change the shape. Some trains show a hollow structure.

Persistent trains are not well understood objects. Several spectra
have been taken in the recent years, which, surprisingly, looks
differently from case to case. The spectra show both continuous
or quasi-continous radiation and atomic lines. The most important
and most persistent line, common for all spectra, is the sodium line
at 5893 A. This suggests that the long-living luminosity is due
to similar mechanism which produces the sodium airglow. The recent
Leonid train spectrum is similar during the first few seconds to a
meteor wake spectrum. The train formed at the position of meteor flare.
The meteor ablation products therefore played an
important role. Nevertheless forbidden lines of neutral and ionized
oxygen were also reported in some train spectra.

4. DAY TIME DUST TRAINS (OR TRAILS) OF METEORS

Trains observed during the day time or twilight after a passage
of a very bright fireball. They may be visible for more than an hour
and change the shape. These trains are visible in the sunlight reflected
(or absorbed) on the dust debris of the meteoroid. During
the night, they may be visible for a short time due the thermal
radiation of the dust or other mechanisms. Dust trains may be formed
at any altitude, depending on the dust deposition by the fireball.
Of course, more dust is produced by massive objects and they often
explode at an altitude around 30 km.

5. METEOR IONIZATION TRAILS (OR TRAINS)

Trails detected using a reflection of radio waves on a column of free
electrons produced by a passage of a meteor. The relation to the
trains detected by optical methods is not clear.



So this is my understanding of the subject. Feel free to forward
it to anybody interested. Since I spent some time writing the text,
I will probably use part of it in a paper.

Best regards


Jiri Borovicka
Ondrejov Observatory
Czech Republic.




More information about the Meteorobs mailing list