How to find extrasolar planets?

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Dec 8, 2011 21:02
It's entirely impossible to directly (optically) observe any extrasolar planets even by the largest space telescope, because they're very far away and too small.
Then how astronomers find them?
The most common method is screening small changes in wavelength of star lights.
Have you ever experienced the following situation?
Sound of vehicles are high when they are approaching, but low when they are passing away, because the frequency of sounds would change.
This phenomenon is known as Doppler shift.
This change in frequency of a wave is not only sound, radio waves are also same as sounds.
Moves of celestial objects cause redshifts and blueshifts.
Stars that have planets move, because they are affected by the gravitation of the planet.
Therefore they show redshift when they're receding from the Earth and show blueshift when they're closing to the Earth.
So astronomers can find extrasolar planets by observing these redshifts and blueshifts.
However, the amount of these redshifts and blueshifts are very subtle and not easy to detect, because the move of the stars are very slow and tiny.
(I've heard that move of sun caused by gravitation of the Earth is almost same as human's walking speed!)
It was almost a fantasy to find extrasolar planets a few decades ago, but advanced technologies have helped astronomers to achieve their detection.
Astronomers have identified over 700 extrasolar planets at present.
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