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Nebulous, wiggly and dark (was Re: (meteorobs) Unusual Geminids)


Folks, just as a follow-up, BOTH nebulous meteors and "wiggly" meteors - and
even their more bizarre cousins, the "dark" meteors - have been touched on at
some length in our list in the past! All are well-observed phenomena, with some
fairly interesting explanations...

Here are my summaries of some of the previous discussions on these strange
sights, all of which you can browse in our 'meteorobs' Web Archive!

    http://www.tiacdot net/users/lewkaren/meteorobs


o Nebulous meteors - which may be seen several times a year - are probably seen
through thin, otherwise unnoticeable cloud layers. But note that during the 1998
Leonid peak (the "fireball shower" of 1998), I saw something quite different
which also fits Jure's description of "a clear central condensation and a coma
or an outer envelope of some sort". Several fireballs during that incredible
night were NOT nebulous - they had distinct, sharp edges. Yet the heads of these
meteors displayed clear comae (sometimes "annular", with central darker areas),
surrounding a more intense, "meteor-like" inner head. This shower was seen
through mostly cloudy conditions for me, however - so maybe the traditional
explanation still applies to my "different" nebulous meteors?


o "Wiggly meteors" - which many observers have noted more than once, mostly
during the peaks of fast major showers such as the PERs and LEOs - are probably
visual effects produced by the persistent TRAIN of a meteor, rather than by any
real variation in the meteor path itself... Because meteor trains are hollow
COLUMNS of ionized air, rapidly expanding from the path of the meteor, they
generally appear foreshortened on their edges (just as a "ring nebula" is in
fact a spherical shell of gas). So trains often give the impression, when you're
fortunate enough to view them in a telescope, of being "twin lines" of light
trailing to either side of the meteor head. If such columns were caught by rapid
sheering in upper atmosphere winds, you'd expect them to collapse in some areas,
shift in others and expand in still others: the result would be apparent kinks
or "wobbles", which MAY occur and dissipate fast enough for the fallible eye to
associate them with the meteor path.

(Keep in mind the minimum velocity for an entering meteoroid is 11 km/s. For its
path to vary even a few degrees from its extremely shallow, "natural" parabolic
trajectory, forces would have to be exerted which would probably disintegrate
most solid materials, let alone the "fluffy stuff" of cometary debris. And upper
atmosphere winds of "only" 0.2 km/s certainly wouldn't do it!)


o "Dark meteors" - which some of us see a fair amount. After hearing many of our
more experienced observers discuss these, I have to conclude they are generally
near-earth objects, especially birds and bugs, seen against a brighter sky
background. This has been confirmed once or twice for me, by my confidently
recording a "real dark meteor", only to hear the sound of a plane, migrating
goose, or dive-bombing mayfly short seconds later... :)


And BTW, I don't mean to completely demystify these phenomena! They are truly
beautiful when you see them, providing a thrill I think is unique to visual
meteor observing. Also, I'm a big fan of never letting the explanation dictate
the observation: if you see an unusual meteor event, ALWAYS try to record it.
However, also prepare yourself mentally to be EXCITED rather than DISAPPOINTED,
should it turn out to be readily explained...

Clear skies and outbursts to all,
Lew


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