"Mike Williams" <nos### [at] econymdemoncouk> schreef in bericht
news:deR### [at] econymdemoncouk...
> Wasn't it Thomas de Groot who wrote:
> >
> >Larry Niven is not talking about a penumbra area in his books, as far as
I
> >can tell. Night comes with the sun gradually cut-off by the shadow
square.
>
> That's exactly what a penumbra is. An observer standing in the penumbra
> sees only part of the sun, the other part being cut off by the edge of
> the shadow square. So the amount of light striking such an observer is
> reduced.
>
Yes indeed, I stand corrected. Furthermore, Niven tells in fact how the
sunlight is reduced during the transition to night. My impression was
however, that it occurred pretty quickly.

Thomas

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