Johann Heinrich von Mädler (29 May 1794, Berlin – 14 March 1874, Hannover) was a German astronomer.

He began giving academic lessons as a private tutor and in this way met Wilhelm Beer, a wealthy banker, in 1824.

In 1829 Beer decided to set up a private observatory in Berlin, with a 95 mm refractor telescope made by Joseph von Fraunhofer, and Mädler worked there.

Beer and Mädler drew the firm conclusion that the features on the Moon do not change, and there is no atmosphere or water.

[3][4] Neither the Tsar nor Orthodox clergy accepted this unsolicited proposal, though a modified version of it was made by Sergey Glazenap in 1900, and ultimately Russia would adopt the Gregorian calendar in 1918.