PICTURING THE PLANETS

Our knowledge of other worlds in the Solar System | has grown enormously since the dawn of the Space Age, along with ever more detailed photographs|

- ANDREW MAY

M ORE THAN 3 000 YEARS AGO, BABYLONIAN ASTRONOMERS I REALISED THAT FIVE BRIGHT points of light moved across the night sky in a different way from all the other stars. These were the planets we now call Mercury, Venus, Mars, Jupiter and Saturn.

In those early days, the only way to observe * astronomical objects was with the unaided eye, which made it impossible to discern any detail. A planet looked virtually identical to any other star, the only difference being its distinctive wandering motion. The very word 'planet' comes from the Greek planētēs, meaning 'wanderer'.

The next major step forward came in 1609, when Galileo first observed the night sky with an early telescope. This showed the planets to be extended discs rather than star-like points of light, and it was only with this discovery that people came to realise that the planets could be other worlds like Earth. As telescopes improved, two further worlds were discovered that had previously been too faint to observe: Uranus in 1781, followed by Neptune in 1846.

The first person to see surface features on another planet was Dutch astronomer Christiaan Huygens, who made a pencil sketch of Mars in 1659. Later observers of the Red Planet spotted white areas around the poles, which were speculated to be ice caps, as well as clouds and evidence of changing seasons. Such discoveries led to fanciful portrayals of Mars as an Earth like world, complete with vegetation and maybe even inhabitants - the latter idea bolstered by the supposed observation of linear features erroneously dubbed 'canals'.

These wild speculations only came to an end in 1964 -just 60 years ago - when a NASA spacecraft finally took the first close-up photographs of the Red Planet.

PHOTOGRAPHING OUR HOME PLANET