Christian Mayer (August 20, 1719 – April 16, 1783) was a Czech astronomer and teacher.
He was born in Modřice, Moravia. He became educated in Greek, Latin, mathematics, philosophy, and theology, although his place of studies is unknown. In his early twenties he decided to become a Jesuit, a path which caused him to leave his home due to the disapproval of his father. He entered the Society of Jesus in Mannheim in 1745. After completing his training he began teaching humanities.
By 1752 his reputation was such that he was selected as a professor of mathematics and physics at Heidelberg. By this age, however, he had developed a strong interest in astronomy. He was appointed Court Astronomer at Mannheim, and was tasked with selecting the instruments for the new observatories at Schwetzingen and Mannheim. With these completed, he was able to pursue his astronomical studies, and published numerous works. In 1769 he was invited to St. Petersburg to observe the transit of Venus, which he did together with Anders Johan Lexell. In 1773, the Jesuit order was dissolved by Pope Clement XIV, and consequently he was removed as Court Astronomer. However he was still able to continue his astronomical observations and studies. He applied for and was granted in December 1765 a Fellowship of the Royal Society.