Edward Walter Maunder (12 April 1851 – 21 March 1928) 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.
Maunder was born in London, the youngest child of a minister of the Wesleyan Society. He attended King's College London but never graduated. He took a job in a London bank to finance his studies.
In 1873 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, 3 sons, 2 daughters and a son who died in infancy. Following the death of Edith in 1888, he met Annie Scott Dill Russell (1868–1947) in 1890, a mathematician and astronomer educated at Girton College in Cambridge, with whom he collaborated for the remainder of his life. In 1895 Maunder and Russell married. In 1916 Annie Maunder became one of the first women accepted by the Royal Astronomical Society in England.
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 studying the work of Gustav Spörer, who examined old records from the different observatories archives looking for changes of the heliographic latitude of sunspots, Maunder announced Spörer's conclusions in his own paper edited in 1894. The period, recognized earlier by Spörer, now bears Maunder's name. Annie worked as a "lady computer" at the Observatory from 1890 to 1895. In 1904, they published their results in the form of the famous "butterfly" diagram that shows this regular variation.
The Maunders travelled extensively for observations going to places such as the West Indies, Lapland, India, Algiers, Mauritius. Their last eclipse expedition was to Labrador  for the Solar eclipse of August 30, 1905 at the invitation of the Canadian government. The expedition was unsuccessful due to overcast conditions.
In 1882 Maunder (and some other European astronomers) observed what he called an "auroral beam"; as yet unexplained, it had some similarity in appearance to either a noctilucent cloud or an upper tangent arc. However, Maunder wrote that the phenomenon moved rapidly from horizon to horizon, which would rule out a noctilucent cloud or upper tangent arc. Further, upper tangent arc cannot occur during nighttime when the observation was made. Since he made his observation during highly intense auroral activity, he assumed it was some extraordinary auroral phenomenon, though one he had never observed again before or after.
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. Maunder was the first editor of the Journal of the BAA, an office later taken by his wife Annie. His older brother, Thomas Frid Maunder (1841–1935), was a co-founder and secretary of the Association for 38 years.
He observed Mars and was a sceptic of the notion of Martian canals. A letter from Maunder was read at the 24th meeting of the Astronomical and Physical Society of Toronto on December 27th, 1892 in which he spoke of M. Flammarion's recent book on Mars as "a most complete and exhaustive monograph". In 1903, Maunder and J.E. Evans conducted experiments at Greenwich using circular disks with Martian surface patterns but no canals on them. Boys from Greenwich Charity School studied the discs at a distance and drew impressions of them which showed canals. The experiment led Maunder to conclude, correctly, that the viewing of canals arose as an optical illusion. (MNRAS, Vol. 63, P.488-499) Flammarion later reproduced the experiment. (Bulletin de la Société astronomique de France, vol.33, pp. 659-660) Maunder was also convinced that there cannot be life "as in our world" on Mars, as there are no temperature-equating winds and too low mean temperatures. Craters on Mars and the Moon, and the minor planet (100940) Maunder  were named in his and his wife Annie's honour.
Maunder was elected a Corresponding Fellow of the Astronomical and Physical Society of Toronto at the 23 January 1894 meeting, after his acceptance of nomination was read out at the 4th annual meeting on 9 Jan 1894.
Mr. Edward W. Maunder, F.R.A.S., First Physical Assistant at Greenwich Observatory, said, "Please assure the Astronomical and Physical Society of Toronto of my sense of the honour they have done me in nominating me as a Corresponding Member and convey to them my grateful acceptance of the position. I fear my somewhat numerous duties will but seldom allow me to contribute to their proceedings, but should I be able, I shall endeavour to do so. The diffusion of a love for Astronomy and the organization of astronomical workers are objects I have much at my heart, and I most sincerely congratulate the Toronto Society on the success they have already attained in these fields."
This was reported in the Journal of the BAA (edited by Maunder) Vol. 4 #1. Maunder was still on the slate as a Corresponding Fellow of the RASC for 1906, in the Proceedings of 1905. His obituary was not published in JRASC.
Posthumously, in 1933 Maunder's Mars experiment was called into question in the JRASC by H. Boyd Brydon, later to become 1st Vice President of the RASC and a Chant Medal winner. Brydon argued for the existence of Martian canals in a response to a chapter by E. M. Antoniadi, "The Illusions of the Canals". Brydon made various accusations against Antoniadi's work in a piece titled, "The Illusions of M. Antoniadi" and cited Percival Lowell's criticism of the Maunder experiment rather than Maunder himself. Antoniadi had been the director of the BAA's Mars section from 1896 to 1917. Antoniadi's response to Brydon, "The Delusions of an Amateur", was printed in JRASC in September 1933, correctly citing Flammarion and complimenting Maunder for his genius, "his infinite honesty and straightforwardness."