Johann Bayer (1572 – March 7, 1625) was a German astronomer.

His great work was the star atlas Uranometria, published in Augsburg in 1603, which was the first atlas to cover the entire celestial sphere. It contained 51 charts, one for each of Ptolemy's 48 constellations, one for the southernmost skies which were unknown to Ptolemy, and two planispheres.

Uranometria introduced the Bayer designations, which are still used today, as well as some of the modern constellations.

The Bayer crater on the Moon is named after him.

Constellations changed by the German Johann Bayer in the 1603 text Uranometria

Centaurus | split into | Centaurus | Crux

Leo | split into | Leo | Coma Berenices

Piscis Austrinus | split into | Piscis Austrinus | Grus

Sagittarius | split into | Sagittarius | Corona Australis

Constellations introduced by the German Johann Bayer in the 1603 text Uranometria

Apus | Chamaeleon | Dorado | Hydrus | Indus | Musca | Pavo | Phoenix | Tucana | Volans

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