On Thu, 31 May 2001 09:08:36 -0400, Bill DeWitt wrote:
>
>"Gail Shaw" <gsh### [at] monotixcoza> wrote in message
>news:3b15ecda@news.povray.org...
>> Cool.
>>
>> Two points. The wells for the planets look a little too deep (compaired to
>> the
>> sun) and the falloff for the planets is too fast.
>>
>> Now do a black hole <grin>
>>
>> What's the isofunction you've used?
>
>    Well that's the problem isn't it... I need a function that doesn't go
>vertical... I would like it to go as deep as the mass is large.

The problem is that the equation for gravity actually does go vertical, if
you're dealing with a point mass.  The equation for gravity in a sphere
is a bit more complex, but it actually goes to zero at the center (which 
means that if any of the various "hollow earth" theories were true, the
inhabitants would experience the sun's gravity without the earth's 
contribution, and points on the inside of the shell would be subject to
some pretty extreme variations in their local "down" vector.  If you left
your beach ball outside, it would soon be traveling at a little under
1000 MPH around the inside of the shell, tracking the sun.)

f'ups to off-topic, since I think the hollow-earth thing is an interesting
topic and it's likely to attract the most comments.

-- 
#macro R(L P)sphere{L F}cylinder{L P F}#end#macro P(V)merge{R(z+a z)R(-z a-z)R(a
-z-z-z a+z)torus{1F clipped_by{plane{a 0}}}translate V}#end#macro Z(a F T)merge{
P(z+a)P(z-a)R(-z-z-x a)pigment{rgbt 1}hollow interior{media{emission T}}finish{
reflection.1}}#end Z(-x-x.2y)Z(-x-x.4x)camera{location z*-10rotate x*90}

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