Johann Bayer (1572 – March 7, 1625) was a German lawyer and uranographer (celestial cartographer). He was born in Rain, Bavaria, in 1572. Two decades later in 1592, he began his study of philosophy and law in Ingolstadt, after which he moved to Augsburg to begin work as a lawyer, eventually becoming legal adviser to the city council there. He had several interests outside his work, including archaeology and mathematics. However, he is primarily known for his work in astronomy; particularly for his work on determining the positions of objects on the celestial sphere. In 1612, he became legal adviser to the Augsburg city council. He remained unmarried and died in 1625.
He is most famous for his star atlas Uranometria Omnium Asterismorum, first published in 1603 in Augsburg and dedicated to two prominent local citizens. This was the first atlas to cover the entire celestial sphere. It was based upon the work of Tycho Brahe and may have borrowed from Alessandro Piccolomini's 1540 star atlas, De le stelle fisse, although Bayer included an additional 1,000 stars. The Uranometria introduced a new system of star designation which has become known as the Bayer designation. Bayer's atlas added 12 new constellations to fill in the far south of the night sky, which was unknown to ancient Greece and Rome.
The crater Bayer on the Moon is named after him.