We have five methods for extrasolar planet detection:
(1) variation in radial velocity of the star, detected via the Doppler shift
(2) planet transit: starlight dims as the planet passes in front of the star
(3) direct visual observation
(4) gravitational micro-lensing
(5) astrometry: small movements of the star against background stars
Image Credit: ESO/A.-M. Lagrange et al.
This composite infrared image of a suspected gas giant planet orbiting the young star Beta Pictoris was taken by the European Southern Observatory's Very Large Telescope in the Atacama Desert of northern Chile. The star has been partially masked to reduce glare, to make the planet visible. The planet is about eight times as massive as Jupiter, and lies approximately 8 AU from the star, well inside the dusty disk that is visible in red and yellow.