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.

-- 
Mike Williams
Gentleman of Leisure

Post a reply to this message