Venus transition, a spectacle on June 6

Venus transition, a spectacle on June 6

It was nothing more than a tiny black drop against the blazing sun; probably similar to “a teardrop in the cheek of time” as Tagore would sing of the Taj.

For it not only occurred in an eight-year cycle once in 105 years, but has raised the curiosity of the astronomers since one of them started to peer deeply into the blue sky in search of celestial objects.

Transits, as R C Kapoor at the Indian Institute of Astrophysics, Bangalore, describes, could technically be a similar event to that of an eclipse where an object, mostly a planet, rolls by between the earth and sun and comes on a straight line between them at some point in that journey. What would perhaps differentiate a transit from an eclipse is the size of the object.

“Transits of planets across the disc of the sun are amongst the most fascinating phenomena in solar system. As seen from the earth, transits of only Mercury and Venus are possible,” Kapoor wrote in his research paper on the Venus transition, scheduled to take place on June 6, the last a living soul would see.

Appear like a dot

Because Venus is much smaller in size, it would appear like a dot as it passes between the sun and the earth. Since the invention of the telescope, there were only seven Venus transitions that happened across four centuries and, as Arvind Paranjpye, Director of Mumbai’s Nehru Planetarium explains, Venus transit was thought to be the best means to calculate the distance between earth and the sun.

“The transit of Venus helped us to estimate the distance between sun and the earth, which is now called one Astronomical Unit (AU),” Paranjpye says.

“Astronomers have figured out the distances of planets from the sun relative to one AU but did not know how to get the value in terms of distance units on the earth such as miles or kilometres. It was Edmond Halley in 1716 who first suggested that observing transit of Venus can be used to find the distance between the sun and the earth.”  It then led to an international expedition in which 150 astronomers stationed themselves in various parts of the world with the sole objective of measuring the earth’s distance from the sun.

Taking part in the international effort was French astronomer Guillaun Le Gentil, who wanted to observe the 1761 Venus transit from the French territory of Pondicherry. His long journey from Europe had to end in disappointment as his expedition was caught in the seven year war between the European heavyweights Britain and France. Gentil’s mission failed as British forces ran over the French and took Pondicherry.

The British had also prepared to observe the two transits by setting up watching posts across India. According to Kapoor, one of them –on the roof of Fort St George in Madras—would have lead to a significant scientific finding but for a curious oversight by the astronomical community of the time.

“Rev William Hirst made a significant observation… of having seen the nebulosity about the planet. That, in fact, was the discovery of the atmosphere   of Venus, duly recorded in his communication as presented in the Vol 52 of the Philosophical Transaction of the Royal Society of London,” said Kapoor.

Excitement amongst the astronomical community returned in the next cycle of Venus transits in 1874-82. Watching the transit with a “six-inch, clock-driven cook equatorial” was Narsinga Rao (1827-92) who had a private observatory in Visakhapatnam inherited from his father-in-law. Rao’s observation was published in the monthly notices of the Royal Astronomical Society.

Besides ensuring the event’s observation from more places in the country, government astronomer Norman Pogson also helped the observers who missed out on account of bad weather by providing “telegraphic determination of respective longitudes”, probably one of the earliest instance of technology being used in a big astronomical event.

The biggest kudos of the 1874 transit, however, belongs to C Ragoonatha Chary, the first assistant to Pogson. Having come from the family of almanac makers, Ragoonatha Chary brought out a booklet titled “Transit of Venus” in English, Kannada and Urdu for better understanding of the celestial event by the public.

The transit skipped a few generation and a full century to happen in 2004. With all technological sophistications, the event was not only well-observed but also well documented, Kapoor says. Given that the next transit of Venus would take place only in December 2117, the experts say that the transit is worth a memory of a lifetime. They also urge not to throw caution in the wind while doing so.

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