6 June 2012 5:00 am Kolkata. I was up in my Saltlake terrace to witness the sunrise, yes sunrise. But it was no ordinary sunrise it was something special, very special, something that wont be witnessed in the next 117 years!!!!!
Yes you have probably got it by know I was about to witness a rarest of rare celestial event, the transition of Venus. It was well past the schedule sun – rise time but the sun was yet to be seen in the heavily polluted sky above the concrete jungle of Saltlake.
It was almost 5:30 am more than a half an hour after schedule sunrise time I got the first glimpses of the sun. It was partially covered by clouds but soon the whole disc of the rising sun emerged out of the clouds. I pointed my Nikkon D60 DSLR fitted with the Sigma 70 – 300 mm (no filter was required) lens and zoomed in at the maximum level and clearly a dot was visible at the 9 O clock position. Yes it was Venus, walking along the disc of the sun.
As I photo documented the rare celestial event, using a x – ray plate as makeshift filter, I was transported back in time and back in 1874 when French scientist Pierre Jules Cesar Janssen also photographed the transition of Venus using a new photographic technique.
The root of the story goes back to early 18th century when Edmund Halley, of Halley’s comet fame, came up with the theory of measuring the distance between the Sun and Earth (Astronomical Unit) by taking advantage of the transition of Venus.
But transition of Venus was not a regular event and Halley left for the heavens in in 1742, 19 years before the next transition of Venus was to take place. Halley used the concept of parallax during the transition of Venus to accurately measure the astronomical unit (AU). Halley wanted to place two observer in the same longitude maintaining a maximum North – South distance, thus taking maximum advantage of the parallax error.
During the next transition of Venus in 1761 voyages were sent all over the world carry out Halley’s experiment. But the scientist came across a strange problem!!!!. It is understood that a exact time of the Venus entering the Sun’s disk is to be noted. But the scientist observed that the circular dot of Venus turned into a water drop shape the moment it entered the solar disc. The phenomena was not only unexplained but also unexpected but it prevented the accurate time keeping and in the proses failed to fined the accurate value of AU.
The phenomena came to be known as “Black Drop Effect” and the scientist were unable to come up with any solution for the next transition in 1769.
For the transition of Venus in 1874 the scientist were more prepared not only they had more advance telescope but they had a new weapon in their armory – PHOTOGRAPHY!!!! Photography was the the most powerful tool of measuring and recording the exact moment of the transition. But shooting multiple frames in a short span of time was something unknown at that time.
Enter Pierre Jules Cesar Janssen, the French scientist who inspired by Samuel Colt’s revolver design, developed the PHOTOGRAPHIC REVOLVER which shot 48 frames per second. Janssen discover not only solve the problem of “black drop” but helped to measure the value of AU with great accuracy. But the story continued and two decades later the Lumiere brothers, used Janseen idea to create the first movie camera leading to the invention of cinema.
“Necessity is the mother of invention” goes an old saying and it is hard to believe that a scientific need of observing a rare celestial event can lead to the discovery of the most popular source of entertainment in the modern world.
As I stood on my Saltlake terrace wondering about the strange coincidence Venus was well into her walk along the solar disc. It was time for another black drop and time for Venus to bid good bye to the Sun only to return after 117 years!!!!!
- Ek Birol Akashjatra r Kahani by Judhajit Dasgupta, Desh 2 June 2012.
- Transit of Venus – a graphic novel
- Prof Biman B Nath: Baman B Nath is a professor of astrophysics at the Raman Research Institute, Bangalore. A talented artist Baman (da) has provided me not only with the sketch of Pierre Jules Cesar Janssen but also provide valuable inputs regarding the transition of Venus.
- Prabir Biswas: Fellow photographer and armature sky watcher, Prabir (da) has provided me valuable tips for photographing the transition of Venus.