[ExI] destiny's road: was RE: rebuilding a saturn v today

spike spike66 at att.net
Thu Mar 31 15:39:29 UTC 2011

From: spike <spike66 at att.net>

>>Interesting thought experiment: imagine the moon to be a perfectly
polished mirror surface of 100 percent reflectivity in all wavelengths.
What would it look like from here?  ... spike


From: extropy-chat-bounces at lists.extropy.org
[mailto:extropy-chat-bounces at lists.extropy.org] On Behalf Of Dan
Subject: Re: [ExI] destiny's road: was RE: rebuilding a saturn v today


>.What about the effect of light from other stars?  Regards,  Dan




We wouldn't be able to see it except during a total eclipse, at which time
the view would be remarkable indeed.  The earth's reflection would appear as
a bright blue dot of apparent diameter of about 300 microradians, definitely
resolvable as a circle, with innumerable tiny pinpoints of light, each about
1% the brightness of star we see.  The reflected images of stars would be
closer together but still approximately the same average brightness at the
perimeter of the polished moon's disk, so that it would form a kind of halo
around the earth's reflection of about 11 milliradians apparent diameter.
That would be a startling sight indeed.


Any other time besides a total eclipse the reflection of the stars would not
be visible, for the same reason we can't see stars in the daytime now.  I
haven't done the calcs, but I wouldn't be at all surprised if the star
images would be drowned out by light from the sun's corona even at a total


A related and interesting thought question would be: imagine the earth
polished to a mirror ball.  What would it look like from the moon?   Again
it would be a point of light always, but brighter, ~4% the brightness of the
sun.  But in a total lunar eclipse, the reflection of the moon would
disappear and we could see the reflection of the cumulative light from a
billion stars, growing brighter toward the periphery to form a 33
milliradian halo, surrounding millions of points of light.










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