THERE'S never been an official title or job description of ''Guardian of the universe'', but if there were, Rob McNaught would be the top candidate. His job is to be vigilant through every night, seeking asteroids and comets headed for a fender bender with the Earth.
Some scientists now accept the extinction of the dinosaurs seems to have been caused by the impact in the Yucatan Peninsula of Mexico by an asteroid from space about 65.5 million years ago. A partly submerged crater about 180 kilometres in diameter was found there late last century to support this assumption.
Furthermore, a thin deposit of the element iridium was discovered in the corresponding layer of Earth's sediments all over the planet. The significance of this is that iridium is rare on Earth but plentiful in asteroids and comets in space.
The impacting body is thought to have been about 10 kilometres in diameter and would have released more than a billion times the energy of the atomic bomb at Hiroshima.
''Even a much smaller body, measuring 100 metres across, could have dire consequences if it fell in a densely populated region, let alone a large city,'' says Astronomical Society of Victoria president Ken Le Marquand.
To work out how much destruction an extraterrestrial impact can have and how far away we would need to be from ground zero to be safe, go to a website hosted by Imperial College London, put in a few parameters and then see the resulting amount of devastation revealed. Scary stuff!
Realising the importance of discovering potential threats from space early, the University of Arizona, funded by a grant from NASA, implemented two affiliated projects for this purpose - the Catalina Sky Survey in the US, covering the northern hemisphere, and the Siding Spring Survey for the southern hemisphere, run from the Siding Spring Observatory near Coonabarabran, NSW.
McNaught is the lone professional astronomer working on this project in the southern hemisphere, monitoring the sky for asteroids that lie below the horizon and out of reach of the Catalina Sky Survey.
''Without this low-cost and highly productive program, there will be a dangerous gap in the search for potentially hazardous asteroids only visible from the southern hemisphere,'' says Dr Nick Lomb, consultant astronomer to Sydney Observatory and the Powerhouse Museum.
McNaught's nightly work involves getting images of 30 seconds' exposure time, covering adjacent parts of sky. He repeats the procedure at intervals, exposing the same field. He uses the Uppsala 0.5-metre f/3.5 Southern Schmidt Telescope, coupled to a 4x4K CCD (camera). Computer software examines the photographs in search of any object that has moved against the background stars, which remain static.
Only solar system objects such as asteroids or comets would change their position and, though man-made satellites produce a trail and are easily discounted, the final processing of the images is performed visually in order to make the judgment call on what the CCD has actually captured.
Since 2004, more than 400 potentially hazardous near-Earth asteroids with a diameter greater than 100 metres have been discovered by the survey.
McNaught has also discovered 75 comets, most of them in the past eight years and the most recent found on November 25 this year.
He is probably best known, however, for discovering the most recent great comet to grace our skies - Comet McNaught, visible here in January 2007.
''Rob McNaught is a 'star' in his own right at Siding Spring Observatory and is recognised as such by amateur and professional astronomers across the world,'' says Professor Bill Leatherbarrow, president of the British Astronomical Association.
In view of all this, it's unfortunate that funding for the Siding Spring Survey is expected to end in January, meaning McNaught will no longer patrol the skies and the telescope and ancillary equipment will be mothballed.
The University of Arizona has decided to put its money into developing new equipment for its own Catalina Sky Survey. Coupled with the appreciation of the Australian dollar, it means the university's funding has dried up for its southern counterpart.
NASA, however, is prepared to put in half the money required to keep the survey going, if another source can be found to provide a matching $55,000 each year to cover salary, overheads and project running costs.
This would seem to be a small amount of money in the grand scheme of things, and the prospective urgency of this continued search. The Australian government has been approached to provide financial support for the project but searching for near-Earth objects doesn't seem to fit in with current plans for Australian astronomy. Perhaps one factor contributing to this short-sighted approach is that the technology needed to avert or prevent a collision between a wandering celestial body and the Earth doesn't exist, so what's the point of keeping a watchful eye on the skies? On the other hand, with good data supplied by the Siding Spring Survey, the trajectory of an intruding asteroid can be worked out and an accurate timing and location of when and where the impact would occur could follow, potentially saving many lives.
''An observed object on an impact trajectory could have the impact predicted to the second and the kilometre,'' McNaught says. ''If mitigation is not possible, evacuations certainly are.''