Friday, 6 March 2009

Maunder on Mars

RH says..... Time to return to Mars, this time focusing on the views of E. Walter Maunder, the head of the Royal Observatory's Photographic and Spectroscopic Department. Maunder seems to have become involved with the debates about the nature of Mars's surface through meetings of the Royal Astronomical Society and the British Astronomical Association, which he had founded in 1890. Since 1877, discussions had tried to account for the differences between the maps produced in that year's heliostatic opposition (the best possible viewing conditions for Mars) by Giovanni Schiaparelli and Nathanial Green.

Schiaparelli map of Mars, based on 1888 observations, image from peacay's photostream, Flickr.Nathaniel Green's Map of Mars, first published in 'Memoirs of the Royal Astronomical Society, 1877-1879.

Green, an amateur astronomer but a professional artist and longtime Mars observer with a powerful telescope, had apparently seen something very different from Schiaparelli, the director of Milan's Brera Observatory but a first-time Mars viewer. Maunder essentially sided with his compatriot and initially agreed that it was most likely that the lines seen by Schiaparelli were the boundaries of differently shaded regions. He became interested in how such optical effects might be produced and, in 1902-03 went to the extent of experimenting on the boys of the Royal Hospital Schools, Greenwich (now the buildings of the National Maritime Museum) to see if images of "canals" could be produced when images without lines were viewed at various distances. His 'Experiments as to the Actuality of the "Canals" observed on Mars' concluded that in most cases,

"the canals of Mars ... are simply the integration by the eye of minute details too small to be separately and distinctly defined. It would not therefore be in the least correct to say that the numerous observers who have drawn canals on Mars during the last twenty-five years have drawn what they did not see. On the contrary they have drawn, and drawn truthfully, that which they saw; yet for all that, the canals which they have drawn have no more objective existence than those which our Greenwich boys imagined they saw on the drawings submitted to them."

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