Astrometry
Minuscule Movements
3 planets discovered
The orbit of a planet can cause a star to wobble around in space in relation to nearby stars in the sky
First, go and read the Radial Velocity text for an explanation of how planets cause their stars to wobble around in space. We'll wait!
Okay, back? Good.
Doppler shifts aren't the only way astronomers can find stars that are wobbling due to the gravity of their planets. The wobble can also be visible as changes in the star's apparent position in the sky.
In other words, scientists can actually detect the star's position wiggling around in space.
Astrometry, as this method is called, is still amazingly hard to do. Stars wobble such a minute distance that it's very difficult to accurately detect the wobble from planets, especially small ones the size of Earth.
In order to track the movement of these stars, scientists take a series of images of a star and some of the other stars that are near it in the sky. In each picture, they compare the distances between these reference stars and the star they're checking for exoplanets.
​If the target star has moved in relation to the other stars, astronomers can analyze that movement for signs of exoplanets.
​Astrometry requires extremely precise optics, and is especially hard to do from the Earth's surface because our atmosphere distorts and bends light.