Venus makes its last transit for the century

About 600 people viewed celestial event from planetarium

Children watching the Venus Transit through telescope at Anna Science Centre - Planetarium in Tiruchi on Wednesday. Photo:M. Moorthy

R. Gajameenakshi said she made a note, in December 2011, to be present at the Anna Science Centre- Planetarium on Wednesday.

“At the winter camp conducted by the Planetarium, we were told that June 6 would be the last time in this century when Venus transits across the Sun,” she said, “and I didn't want to miss it.” Gajameenakshi was among the nearly 600 people who began streaming into the Anna Science Centre since 6.30 am today to witness this rare celestial event.

Since the invention of the telescope in 1609, this is only the seventh Venus Transit that has been observed on earth, according to T. M. Alagiriswamy Raju, Project Director (in-charge), Anna Science Centre- Planetarium. Though Venus made its first contact with the sun's disc at 3.40 am and entered it completely by 3.58 am, the transit could be observed only around 7.03 am- the maximum transit period. The seven hour transit period came to an end at 10.21 am in Tiruchi, when the planet reached its fourth and final contact point. “The contact points, referred to as ingress (entry) and egress (exit), trace the arch followed by Venus while it transits across the sun's disc,” said Mr. Alagiriswamy Raju. Since the transit of Venus cannot be safely viewed with the naked eye or through any lens, the centre had set up multiple safe-viewing methods at their premises: Mylar glasses that use an aluminised solar filter, mirror reflector, sun spotter, welders' glass (shade 14) and telescope projected images. “Our eyes act as lenses as well and the high temperatures involved in this event can completely burn the retina, if viewed directly or through any telescope,” said J.R. Palaniswamy, Senior Scientific Assistant, Anna Science Centre- Planetarium.

In the image thus projected, the planet is marked by a small black dot, while the sun's disc appears like a white and bigger circle enclosing the Venus spot. “I particularly liked observing the phenomenon through the welders' glass because Venus spot appeared the biggest when viewed this way and it was green in colour,” said V. Balaji, one of the observers.