NASA satellites detect a burst of gamma ray energy from a supernova. They relay the exploding star's coordinates to the new facility, called SkyMapper. The unmanned optical telescope rotates to focus on the supernova, one of the most violent objects in the universe. It will take pictures of the blast to add to a collection recording the history and evolution of the cosmos.

Some of SkyMapper's biggest insights, however, are expected to come from more recent events and objects closer to home.

The Australian National University in Canberra is constructing the A$12.5 million telescope – which will start work in September – at Siding Spring, near Coonabarabran in northern New South Wales.

SkyMapper will replace the historic Great Melbourne Telescope, destroyed when the 2003 Canberra bushfires swept through the Mount Stromlo Observatory (see, Storms of fire, Cosmos Online).

With light pollution increasing in Canberra, the university decided to build the telescope at Siding Spring – considered the best dark sky location in the country because of the low level of atmospheric 'shimmer' and its remoteness to coastal clouds.

Near the Warrumbungle Ranges, Siding Spring is the site of the Anglo-Australian Observatory and other major telescopes.

Southern Sky Survey

The telescope's main task will be to conduct the first systematic survey of the entire southern sky to produce a detailed digital map.

Since SkyMapper will be sensitive enough to pick up some of the most distant, faintest objects, the chart will have a deep time dimension.

Because of the time it takes light waves to reach Earth, the Southern Sky Survey will enable astronomers to look back to the time soon after the Big Bang when the first stars' nuclear fusion reactions set the primeval universe ablaze. This was the time when stars were beginning to manufacture the heavy elements from hydrogen, including iron and the element that billions of years later would form the basis of life on Earth.

Another strength of the telescope is a set of coloured glass filters, designed by ANU astronomers and engineers, to analyse the starlight to determine the star's chemical composition, temperature and density. The filters will enable scientists to pinpoint stars with low concentrations of heavy elements, says ANU astronomer Stefan Keller.

"Successive generations of stars return heavy elements to the interstellar gas and this is incorporated in future stars," he says. "SkyMapper will search for stars with the lowest proportion of heavy elements to find the oldest stars. These will give us insight into the way the universe was first lit up by stars and how galaxies form."

These stars are very rare – about 100 in a billion, says Keller.

Rate of expansion

Perhaps the biggest breakthroughs, however, will come from the breadth of the survey rather than its depth, and from objects closer to Earth.

A team led by Brian Schmidt, also at ANU, rocked the astronomy community back in 1998 when it published results of observations of supernovae – the blasts of old stars that have exhausted their hydrogen fuel – suggesting that the expansion of the universe was accelerating.

Previously, it was thought that the recession of the galaxies was decelerating as gravity outstripped the force of the Big Bang that set the universe in motion. The findings raised questions about aspects of

Einstein's theory of relativity and spawned the "dark energy" theory of an anti-gravity force repelling the galaxies.

The Southern Sky Survey will provide the baseline data for identifying supernovae, responsible for at least some of the gamma ray bursts, a phenomenon first picked up in the 1960s by defence satellites deployed by the U.S. to detect clandestine nuclear weapons tests in space.

"We will be able to compare the images from the Southern Sky Survey with images at the site of gamma ray bursts," says Schmidt, who is heading SkyMapper's research program.

Scientists calculate the rate of recession of supernovae from the redshift in the objects' spectra – the push of light towards the red end of the spectrum caused by the expansion of the universe. By comparing the redshifts and distances of nearby supernovae with those of remote ones, scientists can log the change in the rate of expansion since the Big Bang.

However, data on nearby, and, therefore, recent supernovae are lacking. "With current technology, it's easier to find distant supernovae than nearby ones," says Schmidt. "SkyMapper will enable us to look at enough sky to see many nearby ones. You need both to make the measurements."

Trans-Neptunian discoveries

Another project will centre on objects almost on our doorstep – lumps of rock heavier than Pluto and variously catalogued as planetoids, trans-Neptunian objects and dwarf planets. Pluto was demoted from planetary status in 2006 after the discovery of a planetoid more massive than it, and scientists suspect there are other such objects beyond the orbit of Neptune.

"Most observations of our solar system so far have focused on the orbital plane of the planets," says Keller. "Skymapper will look far beyond that and has the potential to detect the biggest planetoids."

The 1.3-metre-diameter SkyMapper telescope will be dwarfed by the 3.9-metre Anglo-Australian Telescope, the biggest optical telescope in Australia. However, technological advances in recent years will give it an edge on conventional facilities, says Schmidt. Constructed by Canberra-based Electro Optic Systems, SkyMapper will be one of only two such telescopes in the world. The other, also built by Electro Optic, is in Hawaii.

The geometry of the curved glass mirrors, manufactured to a precision of a thousandth of a millimetre, and a sophisticated mirror alignment system will give the telescope a wide field of view.

"Normally when a telescope looks at the sky, it looks at a narrow patch which is about a hundredth the size of a full moon," says Schmidt. "SkyMapper will look at a piece of sky 40 times larger than the full moon. In addition, there will be huge digital cameras behind them that are 100 times more sensitive than normal cameras."

Data will be transmitted at a rate of 100 megabytes a second to the ANU's supercomputer facility for processing. The telescope will be fully automated, with the astronomers working from the Mount Stromlo Observatory.

SkyMapper's 11.5-metre-high steel and fibreglass dome has been built and Electro Optic Systems has finished tests on the telescope, constructed at the company's facility in Tucson. The telescope is due to arrive in Australia in early September.

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