HEALTH experts are warning the public not to look directly at the sun at any stage during the Transit of Venus today.
The highly-anticipated astronomical event occurs when the planet Venus passes in front of the sun.
Across South Australia the transit will be visible between 7.30am and 2.30pm (CST) approximately.
SA Health's Public Health Medicine Registrar, Dr Matthew McConnell, says it is important that people do not look directly at the sun without proper protection.
"Looking straight at the sun without protecting your eyes, even for a very short time, can cause serious and sometimes irreversible eye damage," Dr McConnell said. "As there are no pain receptors on the retina, people may not be aware that they are doing damage to their eyes, such as burning their retina. It is important that anyone planning to observe the transit makes sure they are wearing the correct eye protection."
He said people should use solar-eclipse glasses or filters, designed for attachment to spectacles, telescopes and binoculars.
Sunglasses, welders' masks or glasses, photographic film, x-rays, smoked glass, or cameras should not be used - they do not provide sufficient protection from UV rays.
"People can also safely watch the transit by projecting the image onto a piece of paper through a pinhole in a piece of card, while looking away from the sun," he said.
The Astronomical Society of South Australia and CSIRO Education will host a public viewing at the Adelaide Festival Plaza, where people can watch the transit with special telescopes.
RiAus will show the transit live online at livestreaming.riaus.org.au, with vision direct from the Sydney and Perth observatories.
The transit was first observed in 1639 by English astronomer Jeremiah Horrocks.
More than a century later, scientists sailed around the world to measure the transit from different points - the most famous dispatch being the voyage of British Lieutenant James Cook, who took astronomers to Tahiti. The idea was to triangulate the sun's distance from Earth.
Transits occur in pairs eight years apart, then are separated by gaps of 105.5 and 121.5 years. The last transit was in 2004. The next will be in 2117.