What is astrometry? what is astrometry? measuring the positions of stars on the sky using metric units for distance (e. g. meters rather than light years) measuring distances to stars measuring the velocities of stars via the doppler effect searching for planets around stars

Explanation:

It is a branch of astronomy wherein measurements of the positions and movements of celestial bodies are precisely are made.  

For the measurement, minute wobbling of the position of the body is detected. When the shift is detected periodically, the astronomers  come to know that the star is orbited by a planet.  

Also, basic data about the properties of the stars can be collected using this method.

because if the tool that you are using is not balanced it there would be false mass.