New Delhi: Sky gazers in Delhi are all set to witness a rare celestial event Wednesday with Venus - the second planet from the Sun and the Earth`s neighbour - crossing the Sun`s face in what will be a once-in-a-lifetime experience.
Venus will take about six hours to complete its transit, appearing as a small black dot on the sun`s surface, in an event that will not happen again until 2117.
"This celestial phenomenon known as the `Transit of Venus` is one of the most eagerly-awaited events in sky watching. In a transit, Venus passes between Earth and the Sun, appearing through the telescope as a tiny black spot," said an official of the ministry of earth sciences.
According to scientists, transits of Venus occur only on very rare occasions when Venus and the Earth are in a line with the Sun. At other times, Venus passes below or above the Sun because the two orbits are at a slight angle to each other.
Transits occur in pairs separated by eight years, with the gap between pairs of transits alternating between 105.5 and 121.5 years - the last transit was in 2004.
"The occurrence will be visible from anywhere in India. The greatest transit, when the black dot of venus can be observed at the innermost point of the solar disc, will occur around 7:02 a.m. It will be visible in northern India between sunrise and 10:20 a.m.," said C.B. Devgun from SPACE (Science Popularisation Association of Communicators & Educators).
SPACE, an organisation working to spread awareness about astronomy, is taking a scientific expedition having 50 students to Shanghai, China to observe the transit, where it will be visible for the longest time.
In Delhi, the Nehru Planetarium is organising a public viewing with telescope and solar filters being put out at Teen Murti lawns in Chanakyapuri for people to come and watch the rare celestial event.
Some schools in the capital are also organising public viewing in their premises for students to watch the event.
"We will be projecting the transit of Venus through projection and there will be experts to explain students and people about the event," said Sumati Anand, Principal of Gyan Mandr Public School in West Delhi.
A team of the Amateur Astronomers` Association, Delhi, along with the Vigyan Prasar and the Indian Institute of Astrophysics, Bangalore, will webcast the transit from the highest point for such observations - the Indian Astronomical Observatory in Hanle, Ladakh.
The webcast can be viewed live at the NASA Sun-Earth Day website.
Scientists warn people not to watch the sun with the naked eye.
"Do not stare at the sun. Venus covers too little of the solar disk to block the blinding glare. Instead, use some type of projection technique or a solar filter," said Devgun.