.jpg){kind=link}
A life of research
Initially apprenticed in commerce, he taught himself mathematics and astronomy. His orbital calculations attracted Heinrich Olbers’s attention and helped direct him towards research.
He became director of Königsberg Observatory and concentrated on precise stellar positions. Understanding instrumental errors was as important to him as accumulating observations.
Understanding the contribution
Parallax is the tiny apparent shift of a nearby star as Earth moves around its orbit. Bessel selected 61 Cygni, whose large proper motion suggested that it might be relatively close.
Comparing its position with more distant stars allowed him to detect this minute effect. Geometry then supplies the distance: a smaller parallax corresponds to a more distant star.