WARNING: IT IS EXTREMELY DANGEROUS TO LOOK AT THE SUN. SERIOUS EYE DAMAGE MAY RESULT.
A transit will not always occur when Mercury or Venus passes between the Earth and the Sun, as they will usually they pass either above or below the Sun, as viewed from Earth. Transits of Venus are so rare that no one living today has seen one, as they occur only twice in 8 years and then not again for over 100 years. Don’t worry too much if you miss this transit, as there will be another one on 7th June 2012, otherwise you will have to wait until either 2117 or 2125!
The table below provides times of the transit for the capital cities in Australia: (All times are local time)
Observers in Europe, Asia and most of Africa, the transit will be visible from beginning to end, taking a little over 6 hours from start to finish.
There are many explanations for the black drop effect. In previous years, it was believed by some that this effect was due to the atmosphere of Venus (thus an illusion), however, as its atmosphere is too thin to be responsible, we now know that it is not an illusion. The “black drop effect” has also recently been photographed by the TRACE spacecraft during transits of Mercury. Recent explanations suggest the black drop effect may be a combination of blurring caused by the Earth’s atmosphere, with the dimming of the Sun’s disc close to its edge.
The best way to observe the transit safely is to visit your local amateur astronomical society, observatory or planetarium. These groups are likely to be running public viewing sessions for the transit.
If you have a small telescope you can observe the transit safely yourself by using the telescope to project an image of the sun onto a large flat surface. NOTE: DO NOT LOOK THROUGH THE TELESCOPE OR THE FINDERSCOPE, but instead use the shadow of the telescope to aim it directly at the sun, and you should see the Sun’s bright disc projected onto the flat surface.
You may need to adjust the focus of the projected image, until the black spot of Venus can be seen clearly and sharply. The spot will only be about 1/33rd of the Sun’s diameter, however should easily be seen. Viewing the projected image using this method is quite safe, however looking through the telescope will cause instant blindness. DO NOT LEAVE THE TELESCOPE UNATTENDED ESPECIALLY WHEN CHILDREN ARE PRESENT.
During the 2004 transit (for Australian observers) there will be only two moments when the discs of Venus comes into contact with the Sun at a single point. First contact will occur just as Venus initially touches the solar disc. Second contact is at the exact second when Venus has fully “entered” the Sun’s disc.