April 12: Edward Walter Maunder

Edward Walter Maunder

April 12, 1851 – March 21, 1928

Edward Maunder was an English astronomer best remembered for his study of sunspots and the solar magnetic cycle that led to his identification of the period from 1645 to 1715 that is now known as the Maunder Minimum.

In 1873 Edward Maunder returned to the Royal Observatory, taking a position as a spectroscopic assistant. Shortly after, in 1875, he married Edith Hannah Bustin, who gave birth to six children. Following the death of Edith Hannah in 1888, he met Annie Scott Dill Russell (1868–1947) in 1890, a mathematician with whom he collaborated for the remainder of his life. In 1895 Maunder and Russell married; they had no children. In 1916 Annie Maunder became one of the first women accepted by the Royal Astronomical Society.

Part of Maunder's job at the Observatory involved photographing and measuring sunspots, and in doing so he observed that the solar latitudes at which sunspots occur varies in a regular way over the course of the 11 year cycle. After 1891, he was assisted in his work by his second wife, Annie Scott Dill Maunder (née Russell), a mathematician educated at Girton College in Cambridge. She worked as a "lady computer" at the Observatory from 1890 to 1895. In 1904, he published their results in the form of the "butterfly" diagram.

After studying the work of Gustav Spörer, who had identified a period from 1400 to 1510 when sunspots had been rare ("the Spörer Minimum"), he examined old records from the observatory's archives to determine whether there were other such periods. These studies led him in 1893 to announce the period that now bears his name.

He observed Mars and was a sceptic of the notion of Martian canals. He conducted visual experiments using marked circular disks which led him to conclude, correctly, that the viewing of canals arose as an optical illusion. Also he was convinced that there cannot be life "as in our world" on Mars, as there are no temperature-equating winds and too low mean temperatures. 

In 1890, Maunder was a driving force in the foundation of the British Astronomical Association. Although he had been fellow of the Royal Astronomical Society since 1875, Maunder wanted an association of astronomers open to every person interested in astronomy, from every class of society, and especially open for women.

Edward Maunder was the first editor of the Journal of the BAA, an office later taken by his wife Annie Maunder. His older brother, Thomas Frid Maunder (1841–1935), was a co-founder, and secretary of the the Association for 38 years.

Craters on Mars and the Moon were named in honor of him and his wife Annie.