Martian canals
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For a time in the late 19th and early 20th centuries, it was believed that there were canals on Mars.
These were a network of long straight lines that appeared in drawings of the planet Mars in the equatorial regions from 60° N. to 60° S. Lat., first observed by the Italian astronomer Giovanni Schiaparelli during the opposition of 1877, and confirmed by later observers. Schiaparelli called these canali, which was translated into English as "canals". The Irish astronomer Charles E. Burton made some of the earliest drawings of straight-line features on Mars, although his drawings did not match Schiaparelli's.
Some people went so far as to propose the idea that the canals were irrigation canals built by a supposed intelligent civilization on Mars. Percival Lowell was a strong proponent of this view, pushing the idea much further than Schiaparelli, who for his part considered much of the detail on Lowell's drawings to be imaginary. Some observers drew maps in which dozens if not hundreds of canals were shown with an elaborate nomenclature for all of them. Some observers saw a phenomenon they called "gemination", or doubling — two parallel canals.
During the favourable opposition of 1892, W. H. Pickering observed numerous small circular black spots occurring at every intersection or starting-point of the "canals". Many of these had been seen by Schiaparelli as larger dark patches, and were termed seas or lakes; but Pickering's observatory was at Arequipa, Peru, about 2400 meters above the sea, and with such atmospheric conditions as were, in his opinion, equal to a doubling of telescopic aperture. They were soon detected by other observers, especially by Lowell.
During the oppositions of 1892 and 1894, seasonal color changes were reported. As the polar snows melted the adjacent seas appeared to overflow and spread out as far as the tropics, and were often seen to assume a distinctly green colour. The idea that Schiaparelli's canali were really irrigation canals made by intelligent beings, was first hinted at, and then adopted as the only intelligible explanation, by Lowell and a few others. This at once seized upon the public imagination and was spread by newspapers and magazines over the civilised world.
At this time (1894) it began to be doubted whether there were any seas at all on Mars. Under the best conditions, these supposed 'seas' were seen to lose all trace of uniformity, their appearance being that of a mountainous country, broken by ridges, rifts, and canyons, seen from a great elevation. These doubts soon became certainties, and it is now almost universally admitted that Mars possesses no permanent bodies of water.
Other observers disputed the notion of canals as well. The gifted observer E. E. Barnard did not see them. In 1903, J. E. Evans and Edward Maunder conducted visual experiments using schoolboy volunteers that demonstrated how the canals could arise as an optical illusion. [1] (http://adsabs.harvard.edu//full/seri/MNRAS/0063//0000488.000.html) The influential observer Eugène Antoniadi used the 83-cm telescope at Meudon Observatory at the 1909 opposition of Mars and did not see canals, and the notion of canals began to fall out of favor.
The arrival of the space probe Mariner 4 in 1965, which took pictures revealing impact craters and a generally barren landscape, was the final nail in the coffin of the idea that Mars could be inhabited by higher forms of life.
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History of canals
The Italian word canale (plural canali) can mean "canals" (including artificial canals or ducts) or "channels" or "gullies". [2] (http://www.wordreference.com/it/en/translation.asp?iten=canali) This ambiguity also exists in cognate words in other Romance languages such as French (canal), and also in German (Kanal).
The first person to use the word canale in connection with Mars was Angelo Secchi in 1858, although he did not see any straight lines and applied the term to large features —for example, he used the name "Atlantic Canale" for what later came to be called Syrtis Major.
It is often stated that Schiaparelli intended the meaning "channels" and that "canals" was a misunderstanding or mistranslation into English. Nevertheless, the English term "canals" was used from the very earliest accounts in English, and as far as is known, Schiaparelli made no effort to correct the supposed misunderstanding if he was aware of it.
It is perhaps not so odd that the idea of Martian canals was so readily accepted by many. At the time, in the late 19th century, telescopic observers had difficulty distinguishing exactly what they were seeing when they looked at Mars (indeed, it was not until the era of space probes that a clear picture emerged). They saw some lighter or darker albedo features (for instance Syrtis Major) and believed that they were seeing oceans and continents. They also believed that Mars had a relatively substantial atmosphere. They knew that the rotation period of Mars (the length of its day) was almost the same as Earth's, and they knew that Mars' axial tilt was also almost the same as Earth's, which meant it had seasons. They could also see Mars' polar ice caps shrinking and growing with the changing seasons. They interpreted changes in surface features as being due to the seasonal growth of plant life (in fact, Martian dust storms are responsible for some of this). By the late 1920s, however, it was known that Mars was very dry and had a very low atmospheric pressure.
In addition, the late 19th century was a time of great canal building on Earth. For instance, the Suez Canal was completed in 1869, and the abortive French attempt to build the Panama Canal began in 1880. It is perhaps natural that some thought similar projects were being undertaken on Mars.
The notion of a parched Martian civilization building gigantic irrigation canals perhaps inspired H. G. Wells to write The War of the Worlds in 1897, an account of an invasion by Martians coveting Earth's abundant water resources. Even after canals were largely discredited, Martian civilization remained a theme for science fiction such as the Barsoom of Edgar Rice Burroughs (see Mars in fiction).
References
- Wallace, Alfred Russel. Is Mars habitable? A critical examination of Professor Percival Lowell's book "Mars and its canals," with an alternative explanation, by Alfred Russel Wallace, F.R.S., etc. London, Macmillan and co., 1907.
- J. E. Evans and E. W. Maunder, "Experiments as to the Actuality of the 'Canals' observed on Mars", MNRAS, 63 (1903) 488 (http://adsabs.harvard.edu//full/seri/MNRAS/0063//0000488.000.html)
- E. M. Antoniadi, "Sur la nature des »canaux« de Mars", AN 183 (1910) 221/222 (http://adsabs.harvard.edu//full/seri/AN.../0183//0000117.000.html) (in French)
External links
- http://www.theguardians.com/space/orbitalmech/gm_emoi1.htm
- http://www.physics.purdue.edu/astr263l/SStour/mars.html