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(meteorobs) Re: Leonids Meteor Colors
Dear David,
Many thanks for your reply and suggestion for a reason for meteor color
differentiation during the peak of the 1999 Leonids meteor shower.
However, I doubt it that it was reciprocity failure the reason for the
color change during the meteor shower. To start with, my exposures were
neither too short nor too long, the longest being 12 minutes. For ASA 400
film under dark skies and relative low humidity, hence not much background
scattered light, it is not excessively long.
Secondly, different meteor colors are evident in the numerous photographs
of the event I have seen so far, taken by different photographers from
various locations. It is not conceivable that all of them encountered the
same failure.
Finally, reciprocity failure would have affected the negatives in a
consistent pattern, thus I should have noticed consistent color bias
(taking into account that most pictures were exposed for almost the same
amount of time). As different meteor colors are evident from frame to
frame, this possibility has to be ruled out.
I am afraid that the phenomenon is real, hence the explanation should be
sought in the physics of meteor streams or related to atmospheric entry
angle or velocity.
Best regards,
Ilan Manulis
Head of the Small Solar System Objects Section
The Israeli Astronomical Association
==========================================================
At 11:27 01/12/99 +0000, FIPT LBTS1b(con)3, D Cross wrote:
>
>
>>I don't know enough about this topic myself: perhaps one of the photography
>>experts can shed more light, but will reciprocity failure affect the
apparent
>>colour recorded on film?
>>
>>Reciprocity failure means that the usual photographic rule - that opening
the
>>aperture one stop is equivalent to doubling the exposure time - does not
work
>>for *very* long or *very* short exposure times. The point for colour
>>photography is that reciprocity failure affects the different colour layers
>>in the film differently. The net result is a shift in colour balance at very
>>short or long exposures.
>>
>>On the other hand, even though the camera shutter was open for a long time,
>>the actual meteor is only being photographed for a short time. On the third
>>hand, for any given point on the meteors trail, the exposure is very short.
>>
>>Mind you, none of this would explain the _change_ in recorded colour. I'm
>>getting rapidly out of my depth here. Help!
>>
>>David Cross
>>
>>
>>>Date: Thu, 25 Nov 1999 11:23:12 +0200
>>>To: Meteor Observing Mailing List <meteorobs@jovian.com>,
>>> Dr Peter Brown <peter@danlon.physics.uwodot ca>
>>>From: Ilan Manulis <ilan@trendline.co.il>
>>>Subject: Leonids Meteor Colors
>>
>>...stuff clipped out
>>
>>>As it turns out, all meteor trails up to a certain time have a distinct
>>>deep red-purple color. From that time on, they all have green-blue color.
>>>As I took the pictures in succession all through the night, this fact is
>>>evident.
>>
>>
>>
>
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