Overview

At the beginning of the nineteenth century, astronomers knew how far away some objects in the solar system are, but not how far away any of the stars are. During the nineteenth century they measured accurate positions for thousands of stars and gathered their data in catalogs. Their measurements were precise enough to reveal tiny shifts in stellar positions. These shifts resulted not from the motions of the stars but from the motions of Earth in its orbit, and this knowledge allowed several astronomers in the 1830s to measure the distances to several of the closest stars. These distance measurements were the beginning of the work that is at the heart of modern cosmology: the discovery of the size and shape of the universe.

Background

During the...