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Veikko M{kel{: "airglow and nocturnal vision" (Mar 9, 14:06):
>
> Hi-
> Many nocturnal animals have excellent ultra violet
> perception. Where does the UV radiation come from at night
> to allow these animals to use this ability? Is there enough
> UV radiation at the 300-400nm range on the earth's surface
> at night for animals to hunt, navigate, etc?
> I've heard of a phenomena called "airglow" but am not at
> all sure what it is. Can you describe it to me and give me
> an opinion if there would be enough near level UV for
> animals to use?
Airglow is non-thermal, non-auroral electromagnetic radiation emitted by
Earth's atmosphere. It is photon emission from air molecules excited
directly or undirectly by the electromagnetic radiation by Sun. Auroras,
on the other hand, are caused by particle radiation of Sun. Most radiation
from airglow reaches surface as IR radiation, because airglow radiation
originates far above ozone layer. However, they do emit visible and UV
radiation too, and UV radiation observed from space (no UV absorbtion
by atmosphere) is quite strong.
If I recall right, airglow is stronger at southern hemisphere and during
spring and autumn. I have no idea about the sensitivity of the eyes of
nocturnal animals, but one would believe they are sensitive enough, if
they are to hunt during nighttime. Thus would say that airglow is
important
and sufficient source of UV radiation at night.
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