Extrasolar Planet (Encyclopedia of Science)
Extrasolar planets, or exoplanets, are planets that exist outside our solar system. These planets may orbit stars other than our Sun or move independently through interstellar space.
The existence of extrasolar planets has been suspected since the time of ancient Greece. For centuries, however, extrasolar planets existed only in theory because they are extremely difficult to observe directly. Planets shine only by reflected light from the stars they orbit. Because they are so far away from Earth, the faint light they reflect is lost in the scattered light from nearby stars.
The modern search
In the twentieth century, astronomers first tried to detect extrasolar planets by viewing stars that wobble. The motion of celestial bodies is affected by their closeness to other bodies. The gravitational force of one body will "pull" another to it as they pass close to each other. The orbits of the planets in our solar system have a direct effect on the motion of the Sun as it travels through the Milky Way galaxy. Seen from another part of the galaxy, the Sun would appear to wobble as moved along its path. This method only can be used for stars nearest to the Sun because the farther away the star is, the smaller its wobble.
A more accurate method for detecting extrasolar planets is the use of a spectroscope, a device that breaks...
(The entire section is 560 words.)
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