Dubbed Wurdi Youang, the strange stone arrangement was found on property near Mt Rothwell, 80km west of Melbourne - its two points set in perfect alignment with the setting sun on a midsummer's day.
CSIRO experts believe the ancient Aboriginal sundial could be upwards of 10,000 years old, an estimate that would have it pre-date the famous neolithic Stonehenge and the only remaining ancient wonder of the world, the Egyptian Pyramids.
Its location is a closely guarded secret.
CSIRO astro-physicist Professor Ray Norris said the precise alignment of the stones proved it was constructed to map the sun.
"This can't be done by guesswork, it required very careful measurements. If it goes back, let's say, 10,000 years, that predates the Egyptians, the Pyramids, Stonehenge, all that stuff," Professor Norris said.
Wurdi Youang is an egg-shaped ring of stones about 50 meters across. Some of the stones have significant astronomical alignments. For example, some stones seem to indicate the position of the setting sun at the equinoxes and solstices, although there is some disagreement over this idea. Like Stonehenge in the U.K., no records of its use survive, and consequently, nobody knows what it was used for.