About 2,000 professional astronomers from around the world have gathered in Australia for two weeks of discussions.
Their meeting, which began in Sydney on Sunday, is the 25th triennial General Assembly of the International Astronomical Union (IAU).
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The scientists will debate the latest discoveries about the Universe and plans for future observatories.
These include the European projects to build what could become the world's biggest optical telescope in the mountains of Chile, and a giant radio telescope facility in western Australia.
Held every three years, the general assembly of the IAU is one of the largest and most diverse astronomy meetings.
It has been hosted only once before in Sydney, in 1973.
One of the first tasks at the meeting was to give astrophysicist Professor Rashid Sunyaev, director of the Max-Planck-Institut fuer Astrophysik in Germany, the Cosmology Prize of the Peter Gruber Foundation.
The prize, worth US$150,000, is one of the premier international prizes in astronomy.
Dr Sunyaev, a pioneer in the field of X-ray astronomy, was chosen for the award by an international panel of experts for his studies on the nature of the cosmic microwave background - the faint electromagnetic "glow" that still persists from the Big Bang.
"Professor Sunyaev was one of the first scientists to point out the importance of measuring fluctuations in the relic Big Bang radiation as a means of determining fundamental characteristics of the
Universe," said Professor Robert Williams, from the Space Telescope Science Institute in the US and a member of the advisory board that selected Professor Sunyaev for the Cosmology Prize.
Other topics up for discussion in Sydney include:
- The big picture of the Universe: what we know now
- How black holes grow
- The 'dark energy' that powers the expansion of the Universe
- Using lasers to communicate with spacecraft - and what that might mean for astronomy
- Astronomy in Antarctica
- What's special about stars that have planets