"c" == cfs717  <cfs717@tm.net.my> writes:

c> We all know that it is imposibble to see a planet from other solar
c> system nomatter how powerfull a telescope might be.  Because the
c> light from the Star is so bright that it cover-up the dim light
c> from the planet.

That's not quite accurate.  Planets are dim in the optical and
near-infrared so one needs a fairly large telescope just to try to
detect them in the first place.  The issue is how to prevent the light
from the star from "scattering" within the telescope and washing out
the star.  If you have ever looked at an picture of a star, you've
probably seen spikes coming out of it.  Those result from the optics
within the telescope, and they can easily obscure any nearby planet.
The effort in observing planets directly in the optical or
near-infrared focuses on how to reduce this "scattering" so that the
planet can be seen.

c> We also know that a Star emit radio wave.  Won't that radio wave
c> from the Star cover-up the radio wave from the planet where ET
c> live?

We hope not. :)  The issue here is how are the ETs broadcasting their
radio waves.  The Sun and other stars do produce radio waves, and, by
terrestrial standards, they are quite powerful.  However, they
broadcast their power over many different frequencies.  If an ET (or
us for that matter!) chooses a sufficiently narrow range of
frequencies on which to broadcast, outshining the star requires only
late-20th century technology.

By the same token, one can ask what would it take to outshine a star
in the optical or near-infrared?  Again a star is fairly powerful, but
it shines continuously.  If one emits pulses of light, it is possible
with late-20th century or early-21st century technology to outshine a
star for brief instants.  This is the premise behind SETI at optical
wavelengths.

-- 
Lt. Lazio, HTML police   | e-mail: jlazio@patriot.net
No means no, stop rape.  | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html