Greatest transit is at 1.29 GMT on June 6. This transit of Venus will be the last one for the 21st century, the next such event is on December 11, 2117 when many of those who are alive today will not be there to see that.
It will take place across a period of nearly seven hours on June 5-6, 2012, and, for many places, sunrise or sunset will occur while the transit is in progress.
During the transit, Venus will appear in silhouette as a small, dark dot moving in front of the solar disk.
You must have proper eye protection to view the transit. Eclipses glasses and welder’s glass might not be best for this event.
Depending on where you live worldwide, the transit of Venus will happen on June 5 or 6, 2012. If you are a citizen of North America, north-western South America, Hawaii, Greenland or Iceland, the transit will start in the afternoon hours on June 5. And if you live in Europe, Africa, Asia, Australia or New Zealand, the transit will first be seen at sunrise or in the morning hours on June 6.
The last transit in the current century occurred on June 8, 2004. This rare event occurs in pairs, eight years apart, about once a century. Below is a video of Transit of Venus 2004 from SLOOHSpaceCamera:
The Guardian reported that the first observations of a transit of Venus came from Jeremiah Horrocks in Much Hoole, a tiny village in Lancashire. On 24 November 1639, Horrocks watched as the planet traversed the sun after projecting its image on to a sheet of paper through a small telescope. He died two years later aged only 22.
You can learn more about Transit of Venus with the help of this video by ScienceOnline: