The Handy Math Answer Book

and years. The change in wavelength—or the Doppler shift of the light—is caused by the

star orbiting a common center of mass with a companion planet. An example in our own

solar system is the gas giant Jupiter: Its massive gravitational pull causes the Sun to wob-

ble around a circle with a velocity of 39.4 feet (12 meters) per second.

Another detection method is called astrometry, which measures the periodic wob-

ble that a planet causes in the position of its parent star. In this case, the minimum

detectable planet mass gets smaller in inverse proportion to the planet’s distance from

the star. These methods work, and by 2005 more than 150 such planets have been dis-

covered.

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