TECHNOLOGY AND THE UNIVERSE -THE NEW PLANET - UNITED KINGDOM

Pluto's day in the sun

Pluto is known to have five moons. Photo: AFP/NASA/ESA

A TECHNIQUE called ''averted vision'' is used by astronomers to make tough observations and see faint, difficult objects. Pluto is a faint, difficult object.

Some suggest anyone declaring they've seen it in a small telescope must have been using averted imagination.

Pluto is one of the toughest observations that can be made. The usual recommendation is to use an eight-inch telescope from a rural sky; and it would be better if you had a 10-inch. Within the Astronomical Society of Victoria there's a small number of observers who have found it in an eight-inch 'scope and, to the best of my knowledge, only one who got his quarry in a six-inch. The problem is it's smaller than our moon - in fact, two-thirds the diameter and one-sixth the mass. Can't call that a planet. It's so far out in space that light from the sun takes 4½ hours to get there. This makes it very faint and if it were not for photography, I venture to suggest it would never have been discovered visually.

Clyde Tombaugh discovered Pluto in 1930. Photo: Lowell Observatory Archives

There is almost no detail to be seen of Pluto, even in the largest instruments. Much of our knowledge comes from spectroscopic analysis of its light and mathematical computations. It was only relatively recently, in June 1978, that we discovered its moon Charon. The two are in locked rotation, with the same side of each eternally facing the other. In May 2005 two smaller moons, Nix and Hydra, were found by the Hubble Telescope. A fourth was discovered in July last year and a fifth announced two weeks ago.

Of the ''original'' nine planets, Pluto has yet to be visited by a space probe. In a nice gesture, official permission to visit the planet was asked of Clyde Tombaugh, who discovered it in 1930 and the New Horizons Spacecraft was launched towards Pluto in 2006. Taking nine years to travel the 4.7 billion kilometres, it will arrive on Bastille Day, July 14, 2015. As that date nears, the excitement is rising. Tombaugh died before the probe left and among its instrument-crammed load, it's carrying some of his ashes.