Ian Stirling wrote:

In sci.physics Uncle Al <UncleAl0@hate.spam.net> wrote:

Skybuck Flying wrote:

Hi,

Seeing all the bullshit in this newsgroup or maybe sci-fi... or maybe future
technology I thought I add some of mine hehehehe.

My idea is to use the SUN as a way to send a message to aliens ;)

We build a big shield around the sun. And then we can turn it on and off
like a lamp.

Won't work.  Shield reaches equilibrium temp and emits.  Who is going
to launch it, NASA?  Ha ha ha.

Do the numbers before you laugh idiotically.
A shield around the sun at the diameter of the earth would reach
around 0C.

(there are engineering difficulties.)

   That's a point Skybuck seems to miss. You can block the Sun with your
thumb at arm's length, but at interstellar distances, if you don't want
to be a dot of less-than-planetary diameter crossing the Sun (which
itseld is hard enough to detect), the (presumably disk shaped) shield
has so be somewhat larget than the solar diameter, and will still
obscure the Sun completely, only in one not-very great angular
direction.

   Anything that can obscure more of the Sun, gets into structures like
Ringworlds and Dyson Spheres, which have stability issues with respect
to the central star.

   ...oh, and they require (ahem) slightly more mass than can be
launched on a space shuttle.

   And again, assuming it has slats not unlike a venetian blind, or a
Naval Morse Code signaling light, imagine trying to make a structure
(which can never be perfectly rigid) like that, but millions of miles
wide, open and close at a useful rate....

-- 

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