Planetary astronomy was transformed by the Italian scientific genius Galileo Galilei in 1609. Before Galileo the planets were merely points of light that periodically moved around against the background of stars. Plotting positions and endeavouring to calculate orbital parameters was the main occupation. Galileo’s new-fangled astronomical telescope changed everything. The Moon, instead of being a perfectly smooth sphere, as Aristotle had suggested nearly 2000 years before, actually had mountains, craters and ‘seas’; Saturn was girdled with an equatorial ring and Jupiter had four small satellites.

The years 1781, 1846 and 1930 saw the solar system dramatically expand, these being the years in which Uranus, Neptune and Pluto were discovered. As telescopes increases in size and sophistication more and more planetary surface details were revealed. A major breakthrough occurred in 1878. Giovanni Schiaparelli, the director of the Milan Observatory and a man with super eyesight, used his meticulous observations of Mars to produce a map of the surface. This seemed to be covered in groove-like channels. In Italian the word is ‘canali’. Impetuous English speakers immediately translated this as ‘canals’ and soon other planetary astronomers, such as the rich American Percival Lowell, were producing books and articles that overflowed with descriptions of artificial waterway constructed by intelligent Martians irrigating the equatorial regions of their planet with water from the melting polar ice-caps.

Planets were big news, they were alive, they were fascinating, they must be studied in detail and we must try and devise ways of visiting them. The likes of Jules Verne and H. G. Wells soon had us worrying about interplanetary conflict and interplanetary cooperation.

A century ago science fiction was obsessed with travel and contact, and we read of sending people to the centre of the Earth, the Moon or beyond, as well as receiving visitors from nearby planets. But until recently astronomy has been very much a ‘hands-off’ science. Astronomers have been able to look but not touch. They stand at the bottom of the telescope and have to accept what arrives down the end of the tube. But Sputnik 1, launched by the USSR in October 1957, changed that - especially for solar system astronomers. The space age and space race started. Large rockets were developed that could hurl space probes way beyond the Earth’s atmosphere, past the Moon and the planets and out towards the stars. Soon those rather fuzzy, turbulent, indistinct images of planetary surfaces, taken from huge distances, were being replaced by crystal-clear close-ups.

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Content last updated: 06/12/2004

Prof. David Hughes

David Hughes is Professor of Astronomy at the University of Sheffield and has worked there since 1965. Professor Hughes has published well over 200 research papers concentrating on the solar system and especially the minor bodies such as asteroids, comets, meteorites and meteoroids, and their origin, decay, size distribution and evolution. Hughes' ground-based and spacecraft observations of Halley's Comet led to an interest in the work, life and times of Edmond Halley and the history of astronomy in general. Hughes enjoys giving popular lectures, reviewing books and has had asteroid number 4205 named after him. At present he sits on the Council of the Royal Astronomical Society and the Swedish Space Research Advisory Committee.

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