People across the world witnessed Venus transition, a rare astronomical event, on Tuesday and Wednesday. Such an event will not occur again for more than a hundred years.

Venus transition occurs when Venus passes between the sun and the earth. Students and several people saw the Venus as a small dot slowly drifting across the face of the sun.

Venus was visible in most of the places across the world. The transition began in North America at the 22:09 UTC on Tuesday. Several people in America saw the event using solar eclipse glasses, welding glasses and pinhole cameras.

In Mexico, at least 100 people lined up two hours early to view the event through telescopes or one of the 150 special viewing glasses on hand, officials said. Observation points were also set up at a dozen locations, according to the Daily Mail.

Today, Wednesday, most of the people in South Asia, East Africa and most of Europe have witnessed the event. In Britain, the Venus transition began at 4:30 BST.

Throughout history several astronomers have witnessed this sort of event. Since 2000 B C, 53 transits have occurred; among those only six have been witnessed since the invention of the telescope in 1608.

In 1639, Jeremiah Horrocks and William Crabtree, two astronomers from England, were the first to observe and record the Venus transition.

In 1769, several astronomers conducted a survey to gather transit data from various locations around the world that were later used to calculate the distance between earth and the sun, thereby establishing the solar system's scale.

"Throughout history, astronomers have creatively used nature's coincidences as opportunities to learn something new about the universe," said Natalie Batalha, scientist at Nasa Ames Research Center, Moffett Field, in a statement. "Today is no different. As Venus crosses the disk of the sun, her shadow sweeps across the face of earth in the same way that the shadows cast by distant exoplanets sweep across the face of the Kepler photometer."

Nasa had broadcast this rare event from several places across the world.

Here are some pictures of Venus transition 2012:

NASA image shows the planet Venus at the start of its transit of the Sun.Reuters
The planet Venus transits in front of the sun outside Salt Lake CityReuters
People look at the planet Venus transiting across the sun over AmmanReuters
The planet Venus is seen as a black dot as it makes its transit across the sun over AmmanReuters
A woman helps her child hold a solar filter as he looks at planet Venus transiting across the sun at a public viewing at the Singapore Science CentreReuters
Planet Venus transits across the sun in Singapore.Reuters
Venus transits across the sun as seen over Hong Kong.Reuters
Venus transiting across the face of the Sun. This image was taken by the Solar Dynamics Observatory (SDO).Reuters
The planet Venus makes its transit across the Sun as seen from KathmanduReuters
Venus transition seen in Beijing.Reuters
Venus starts its transit across the sun as seen from Newcastle.Reuters
The planet Venus makes its transit across a setting sun on the Pacific Ocean in Encinitas, California.Reuters