This is known as parallax. If we know the distance between both eyes and the angle from each eye to the finger, we can calculate the finger's position by triangulation. Another important yardstick can also be determined from Hipparcos data - the proper motions of the stars. The proper motion is the real movement of the star across the sky and is a partial reflection of its motion through space relative to the Sun. Usually, the further the star, the smaller its proper motion.
Astrometric measures are of fundamental importance in many areas of astronomical study.
For example, they allow astronomers to learn about the structure of our Milky Way galaxy, and to calculate the distance scale of the universe. Another problem is that stellar parallaxes are very small since the stars are so far away. From the ground the most accurate measurements have been to a precision of about 8 milli-arcseconds. These problems were overcome when Hipparcos went into orbit. As a result, the number of stars for which a direct measurement of distance is known has dramatically increased.