World first: Aussie astronomers digitally map southern sky

Digital map of southern sky available free online through a ‘virtual observatory’.

The Australian National University (ANU) is conducting a world-first program to digitally map the southern sky using a specially constructed telescope called Skymapper, and in another global first will provide the data free to the world via a virtual observatory.

Skymapper is the first of a new breed of dedicated "rapid survey" telescopes, built by the ANU's Research School of Astronomy and Astrophysics (RSAA) at Mount Stromlo observatory in Canberra.

Funded by insurance from the January 2003 bushfires that destroyed most of Mount Stromlo's telescopes, the Skymapper project will take five years to map the southern sky and when finished will have created Australia's largest non-proprietary data set - a whopping half-petabyte of astronomical information.

"Telescopes such as Skymapper are really a portend of a shift in how we will do astronomy in the future," said Stefan Kellar of the RSAA.

"We will see an increasing reliance on globally distributed Web-based datasets that will be brought together by the concept of the 'virtual observatory'," he said.

Skymapper will have a huge scientific impact because it is covering such a large area of sky, something that has only recently become feasible.

"Prior to a few years ago the only way we could perform something like a southern sky survey was with photographic plates, which are rather insensitive and hard to characterize, so the science we can extract from them is rather limited," Kellar explained.

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The Skymapper telescope will be housed at the ANU's Siding Springs observatory and will be a fully automated, remote facility capable of calibrating and adjusting itself throughout the night to adapt to prevailing conditions.

"The preoccupation of the Skymapper will be the Southern Sky Survey, which will be a five-year multi-colour and multi-epoch survey of the entire southern sky," Kellar said.

Everything south of the celestial equator will be imaged in six filters, with each filter having six exposures allowing astronomers to build a map of what the sky looks like in different colours, as well as seeing how it changes over time.

The telescope will generate around 0.8 terabytes of data per night, with one image required every 20-25 seconds.

Skymapper's focus will extend from nearby solar system objects all the way out to the edge of the optically observable universe, some 12.8 billion light years away.

"In that dataset we can extract those extremely rare but very important objects that have eluded us thus far, that give us important constraints on the typical parameters of the universe," Kellar said.

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But Skymapper wont just be a content provider for the southern hemisphere; it also boasts a specific niche in stellar astrophysics - the characterisation of stars.

"There are three important parameters that define a star: temperature, surface gravity, and heavy element abundance," Kellar explained.

Those parameters can tell astronomers and astro-physicists how and where these stars were formed, and how they got to where they are today.

"We've designed our filter set to have optimal ability to decode those stars. It's a whole new window into the construction of the galaxy," Kellar said.

The data collected by Skymapper will flow through the Siding Springs Observatory and onto the ANU's Supercomputing facility, where a range of open source software is used to process and monitor the calibration of the system.

One of the things the RSAA is most proud of is the fact that this world-first information base will be made widely available, free of charge, to anyone who wants it.

"We have so much data and in order to make the most of that we have to let the rest of the world do great science with it as well as ourselves, so we will share that via the Web in the order of 30 terabytes," Kellar said.

Skymapper will also improve the effectiveness of other instruments by providing calibration anywhere in the sky.

Kellar said the Southern Sky Survey should be up and running by the middle of 2008, and the data Skymapper provides "will be used in countless science projects, not only here but all over the world".

The only problem? The Sliding Springs observatory is located in one of the highest lighting strike areas in Australia.

"One strike would cook it," Kellar said.

(Andrew Hendry was a guest at the ANU's Research School of Astronomy and Astrophysics)