http://www.ustream.tv/channel/transit2012
AMAZING!!! // Remember not to look at the sun!
The incredibly rare transit of Venus has begun, and health officials are reminding people not to look directly at the sun during the astronomical event.
Opthamologists warn that staring directly at the sun can cause profound but initially painless eye damage.
Even looking at the sun through welding glasses does not offer enough protection.
The event occurred last on June 8, 2004, and will not happen again until December 11, 2117.
Only six transits of Venus are known to have been observed since humans identified the phenomena: in 1639, 1761, 1769, 1874, 1882 and 2004.
The event holds special significance for Australia.
Captain James Cook travelled to the island of Tahiti in 1769 to observe the transit of Venus. It was on that expedition that he later discovered the east coast of Australia.
Surveying and Spatial Sciences Institute surveyor Chris Swane says little was known about the transit until 17th century astronomers began to study planetary distances.
"They had a fairly good idea about where the stars were or the names of the stars, the different constellations, and they even knew the ratio of distances between the planets and the Sun," Mr Swane told AAP.
"But they never knew the actual distance between the Earth and the Sun."
The development of the three laws of planetary motion by the famous 17th century German mathematician and astronomer Johannes Kepler changed all that.
Later, astronomers observed the amount of time it took Venus to cross from one side of the sun to the other side and used the laws to work out the distance between the Earth and the sun.