KARACHI, June 8: The scientists and students at the University of Karachi, like people elsewhere in the region, observed Venus as a black dot crossing the surface of sun on Tuesday.

Research students under the supervision of their respective teachers visited the observatory in the campus in groups. They were seen excited after seeing the transit of Venus across the face of sun, a rare astronomical event which took place after 121 years and six months.

The transit of Venus across the sun's disk was like a solar eclipse and was visible right from the beginning (i.e. its first exterior contact with the sun at 10.17am), said a student, adding that it took Venus about six hours to complete its transit.

As per the observatory staff, Venus entered the solar disc from southern part of the rim and travelled across it towards west. They said that Venus reached closest to the centre of sun at 1.19pm.

It came into the third contact (Egress Interior) at 4.02pm when it was completely inside the solar disc, but touching the outer rim of the sun. The fourth and the last contact was observed at 4.21pm when the Venus was completely displaced from the solar disc, they added.

Talking to Dawn, the Institute of Space and Planetary Astrophysics director, M. Shahid Qureshi, said that each contact took place at the pre-calculated time. The "Black Drop" effect due to the atmosphere of Venus was clearly visible at both the second and third contacts, he added.

A number of citizens had made arrangements to observe the rare event. People on streets and roads were seen using X-ray films and welding glasses to see the movement of Venus.

Children were mostly not allowed to go in open sky and see the transit with naked eyes.Experts had advised the citizens not to see the transit with naked eye instead they should use binocular, welding glasses, or a telescope with appropriate solar filter.