Eric,
	Good post.
The science fiction writer E.E. "Doc" Smith proposed modulating the output
of a star, our own Sun, in the Lensman Series.  These six books were
written about 1940 or so, and that series is the ultimate of sci-fi
space-operas.  This book series inspired the TV series "Babylon 5".  
	"Doc" had Sun-orbiting conductors that were energized to briefly focus
Solar energy (most of it) into a beam weapon, to defend Earth against an
invading fleet.  If you know vacuum-tube electronics, this is actually
somewhat realistic.  
	You are probably familiar with charged wire/charged grid beam-steering
technology; in most homes, it is called TV.  Unless you have a flat-screen
monitor, you also have similar magnetic or electrostatic fields in your
monitor that focus the electrons of the computer-display (Cathode Ray Tube
or CRT) into a picture.  Focusing all solar output could "beam" some rather
noticeable intensity in one direction, and that would "dim" the output in
all other directions.
	That much beam energy could quickly vaporize an Earth-crossing asteroid:
we could even save ourselves from the threat that may have wiped out the
last big dinosaurs.  :-)
-- 
Cheers,
Red
--
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Eric Albers wrote:

Since we know that stars are excellent at being seen from very far
away, would a civilization slightly more advanced use some kind of
modulation on their star to send a message out?

While this may seem silly, as even a 10km x 10km shutter is very tiny
relative to the size and surface area of our star, what size would be
needed to be easily detected from afar?

We are already measuring the 'wobble' of stars to infer a planets
existance, could a toggling of the stars brightness, albeit a tiny
one, or one in only a narrow frequency band, be a more effective means
of transmission, given that effective is partially defined as 'easily'
seen/interpreted?

Eric Albers

e r i c at ericalbers dot com