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Re: (meteorobs) Re: Zodiacal light


Mike Linnolt writes (in indirect answer to my question):

>However [the Gegenschein's] visibility seems to vary from day to day
>and season, so you just may have tried during a "poor" time.

I definitely have to agree with this: in fact, both the Zodiacal Band and the
Gegenschein may vary in appearance from night to night, even under very similar
circumstances! Obviously, these variations in visibility seem to indicate a
strong but subtle dependence on small variations in the sky contrast at a given
observing site, even across relatively short time periods...

During just this past year's Leonid campaign in South Florida, I recall two
successive nights in the Keys with very similar Limiting Magnitudes: in between,
the Gegenschein changed from a large 25o-by-15o haze with what appeared to be a
complex shape streaming directly into the brighter areas of the Zodiacal Band,
down to a little 15o-by-8o "kernel" of simple oval shape, disconnected from the
barely visible "remnants" of Zodiacal Band elsewhere on the Ecliptic.


One note of interest to meteorists: if you think of it, Gegenschein is actually
far easier to explain by "common sense", than either the Zodiacal Light or the
Zodiacal Band are. After all, Gegenschein is the "backscattered" light of the
Sun (i.e., a simple reflection) whereas both the ZL and ZB require side- and
even FORWARD-scattering of that light.

In fact, the brightness of Zodiacal Light relative to the Gegenschein or the
Zodiacal Band is evidence of a quite unusual property of the fine dust which
makes up the Ecliptical band: due to their tiny average size, these particles
are better at FORWARD-SCATTERING visible light than reflecting it.

Interestingly, if the distribution of particles among Ecliptical dust were only
slightly different - tending more toward the large particles which make up many
meteor shower streams, for example - I believe the Gegenschein would appear far
larger and brighter than it is, and the Zodiacal Light which so many of us can
see so easily would be far less visible.


BTW Mike, where is White Mountain exactly? I don't recall hearing of it.

Take care,
Lew


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