In Searches for Planets Orbiting Stars Other Than the Sun

Multiple Choice

In searches for planets orbiting stars other than the Sun, what is the astrometric method?

A) searching for tiny "bumps" on images of a star, due to the light from a planet located close to the star
B) searching for tiny displacements of the infrared image of a star compared with its optical image, caused by the presence of planets that are cool and emit primarily in the infrared
C) searching for tiny wobbles in the position of a star, due to the gravitational pull of a planet orbiting around it
D) searching for tiny wobbles in the positions of absorption lines in a star's spectrum, caused by radial velocity variations of the star as the result of a planet orbiting around it