Stellar wobble is a variation in the position of a star

Star

A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

 due to the gravitational influence of another body orbiting it. Stellar wobble is visible as a Doppler shift

Doppler effect

The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...

 in the star's spectrum or as a motion of the star in the plane of the sky. The Doppler shift is caused by the star moving towards and away from the Earth as it and its companion(s) orbit around their common center of mass

Mass

Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

.

Stellar wobble is an important phenomenon in astronomy, as it can be used to detect extrasolar planets and black hole

Black hole

A black hole is a region of spacetime from which nothing, not even light, can escape. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. Around a black hole there is a mathematically defined surface called an event horizon that...

candidates. Currently, the majority of extrasolar planets have been detected using the Doppler shift method, but several astrometric programs are being developed which are designed to measure the motion of the star in the plane of the sky.