"Alain" <ele### [at] netscapenet> schreef in bericht
news:43603cc3$1@news.povray.org...
> >
> In the images I saw, the shadowing squares are between 1/2 and 2/3 of the
ring's radius. With such
> proportions, you have prety whide penumbraes.
>

According to Larry Niven, in Ringworld, the shadow squares are 1x10^6 by
2.5x10^6 miles big, and orbit the sun at about 12x10^6 miles from the
primary. Now, this last figure seems to be wrong. According to my building
in Moray, they should orbit at about 16x10^6 miles so that day and night
areas are about the same size.

An area light for the sun is needed indeed. I used a glow (for latter
purposes), but I shall experiment further.

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.
Which doesn't exclude a penumbra of course.

Thomas

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