Modern astronomy seems dominated by huge, expensive and powerful machines staffed by highly trained professionals. Yet significant findings can still be made by people like Anthony Wesley, a computer software engineer and amateur astronomer who lives just north of Canberra.

About 12.40 am on 20 July 2009, Anthony—who loves to keep an eye on Jupiter with his 14.5 inch (36.83 cm) diameter reflecting telescope— noticed a small black spot near the south pole of his favourite planet. It was in the wrong place and the wrong size to be a moon, he says, and also it was moving too slowly. In fact, it was moving at the same pace as a nearby storm.

The only possibility that fitted the facts was that he was observing the debris from a collision between a fast moving body, such as an asteroid or comet, and the planet itself. But the chances of that were remote. It was an event that had only ever been seen once before, almost exactly 15 years previously when the comet Shoemaker-Levy slammed into Jupiter.

With some trepidation Anthony emailed astronomers around the world; his suspicions were soon confirmed. The professionals then used their analytical machines to determine the composition of the dust and the impacting body, as well as the force of the explosion—all very valuable information.

That should have been enough for one lifetime, but in early June 2010, Anthony did it again, glimpsing a flash of light near Jupiter’s edge. A colleague in the Philippines quickly confirmed the sighting which turned out to be the fireball of an asteroid about ten metres in diameter burning up in Jupiter’s atmosphere.

PHOTO: THE DARK SPOT ON JUPITER FIRST DISCOVERED BY AMATEUR ASTRONOMER ANTHONY WESLEY, AS PHOTOGRAPHED BY THE HUBBLE SPACE TELESCOPE ON 23 JULY 2010. CREDIT: NASA/ESA/H. HAMMEL (SPACE SCIENCE INSTITUTE, BOULDER, COLO.)/THE JUPITER IMPACT TEAM.

Anthony Wesley, Tel: +61 (2) 6227 0891, awesley@acquerra.com.au, acquerra.com.au/astro