Light of knowledge

Published : Sep 11, 2009 00:00 IST

In the light of knowledge attained, the happy achievement seems almost a matter of course, and any intelligent student can grasp it without too much trouble. But the years of anxious searching in the dark, with their intense longing, their alterations of confidence and exhaustion and the final emergence into the light only those who have experienced it can understand it.

- Albert Einstein

VERY often people lament the declining interest in science among the young at the undergraduate level and beyond. Students are generally blamed for pursuing disciplines that offer lucrative prospects such as information technology and management. This may be partly true, but the fact is that there are a whole lot of them out there with a keen interest in science who end up losing it thanks to unimaginative course syllabi and the system. The bulk of science teachers, too, lack the initiative to put in that extra bit that can sustain the students interest and are generally content with following the rut. With some imagination and effort, the students initial enthusiasm for science when they enter colleges can be properly channelled and their intrinsic talent nurtured. The total solar eclipse (TSE) of July 22 provided one such example of how a teachers dedication can motivate young students to do things beyond the ordinary. The fact that this is the International Year of Astronomy (IYA) adds to its significance.

The vision of IYA 2009 is to convey to the people the excitement of discovery and stimulate interest especially among the young in astronomy and science under a central theme: The Universe, Yours to Discover. A dozen young undergraduates of Sri Venkateswara (SV) College, Delhi University, certainly did discover the magic of a TSE and all its various spectacular effects all by themselves. Their physics professor, Pranjal Trivedi, guided them, instilled in them the thrill of building instruments and made them experience the spirit of scientific discovery. Most of the students involved were girls. As the college press release put it, the entire expedition was also an invaluable learning experience in how science actually works for the students.

The path of totality of this rare TSE indeed, the TSE of this century was a 200-metre-wide belt that started from near the Gujarat coast and, passing through central and northern India and over Assam and Arunachal Pradesh, moved over China and the Pacific Ocean. It was rare because of the long duration of totality. The maximum duration of totality anywhere on the path was over the ocean about 100 km south of Bonin Islands, south-east Japan, and it lasted six minutes and 39 seconds. The next eclipse that will surpass this duration is due on June 13, 2132. Only the eclipse of June 20, 1955, which lasted seven minutes and 28 seconds over the Philippines, surpassed the TSE of July 22. The maximum theoretical duration of a TSE is seven minutes and 31 seconds. The duration of the July 22 TSE was between three and four minutes along the path over India. Not surprisingly, the eclipse generated enormous interest in India, among both amateur and professional astronomers.

But there were two major apprehensions about viewing the eclipse over India. One, it came at a time when the monsoon is usually vigorous along the totality path. This is what happened during the 1999 eclipse, which was clouded out even over Bhuj in the dry Kutch region of north-western India. Second, the eclipse was happening just after sunrise, which means the sun would be at a low altitude. So the likelihood of cloud cover, on the one hand, and the low angle of the sun over the horizon at the time of totality, on the other, were clear dampeners to an otherwise cosmic spectacle.

As it happened, the eclipse over India was almost washed out except at a few locations. One of the prominent places where the TSE was seen for its entire duration was Varanasi, which was somewhat unexpected given the sunshine probability of only 10-20 per cent there. Taregna, about 40 km from Patna, which was touted as the best location for watching the eclipse and where a huge number of people had gathered, was completely clouded out.

Given this uncertainty, major scientific teams from India went to a place called Anji in China, where sunshine probability was 60 per cent. The experiments to be conducted there by the Indian Institute of Astrophysics (IIA), Bangalore, for example, were aimed at studying the waves in the solar corona. But not to miss the eclipse over India, the IIA deputed scientific teams to Varanasi and Arwal near Patna. The IIA set up experiments to study the shadow bands, and for videography of the eclipse at Arwal and for white light photography at Varanasi. At Varanasi, a team from the Banaras Hindu University joined the IIA team and they set up camp at Saamne Ghat. The Varanasi team was very lucky.

(Solar corona is the plasma atmosphere of the sun, extending millions of kilometres into space, most easily seen during a TSE. It is hotter by a factor of 200 than the visible part of the solar surface. The photosphere is about 6,000{+0}, whereas the corona is about one to three million degrees. The mechanism by which the corona is heated is still unclear. Waves in the corona refer to the sonic pressure waves that are believed to cause the heating. Since the corona is a trillion times less dense than the photosphere, coronal light is a million times less bright than the sun and is normally swamped by the suns brightness. The faint corona becomes visible when the photosphere gets totally covered during an eclipse. A thin layer of chromosphere separates the corona from the photosphere. Besides the corona, the chromosphere and the solar prominences, which are bright loop-like structures that extend from the photosphere into the corona and whose origins are unclear, are also seen during an eclipse. Shadow bands refer to a curious eclipse phenomenon that is sometimes observed while a small crescent of the sun is still visible, when thin wavy lines of alternating light and dark can be seen moving and undulating in parallel on plain light-coloured surfaces. These were observed very clearly, for example, at Raichur during the 1980 eclipse.)

There was also collaboration with the Indian Air Force to fly from Gwalior on a Mirage 2000 aircraft at about 1,400 metres into the path of totality to take pictures. The aircraft mission would, presumably, have been successful as it would have flown above the clouds. Since the Patna region had been clouded out, it is not clear whether the Arwal mission was successful.

The Varanasi mission was apparently successful as, according to the IIA website, the clouds opened for the ground-based observations just as the time of the second contact (C2) approached the time when the solar disc is about to be entirely covered by the moon.

While only the picture of totality from Varanasi has been posted on the IIA website, presumably equally good pictures of the diamond ring and Baileys beads, which the teams witnessed, have also been obtained. (When the shrinking visible part of suns photosphere is about to disappear behind the moon, Baileys beads occur. These are caused by the sunlight that still filters through the lunar valleys but is blocked by mountainous regions. Totality then begins with the diamond ring effect when there is the last bead and one sees the last bright flash of sunlight.)

The remarkable thing about the SV College students expedition is that, given the general low expectations of being able to see the TSE over India, they went about identifying the place to observe the eclipse in a systematic and scientific manner. They chose a place called Mohaniya, a small town in Kaimur (Bhabhua) district of Bihar (about 80 km from Varanasi). This turned out to be an excellent site.

Trivedi and the students studied the weather predictions for July along the track that the famous eclipse trackers J. Anderson and F. Espenak of the University of Manitoba, Canada, had made on the basis of archival records of the weather. On the basis of historical cloud images of July 22, it was found that there was a dip in the fraction of clouds somewhere near Patna, more towards the plateau and not as far near the plains, explains Trivedi.

An advance trip to survey various places south of Allahabad and Varanasi in this region, like Reva, Roberts Ganj and Mohaniya, was undertaken. Mohaniya was chosen after considering all factors, including the elevation of the sun at the time of the eclipse, its clear visibility from a suitable place, and other logistics, most importantly the absence of large, disturbing crowds.

The students group comprised nine girls and three boys from the II and III year B.Sc. courses. The fact that, besides physics, it included three from chemistry and one from electronics is indicative of how astronomy kindles interest across disciplines among the young. Even though the students had little prior astronomy experience, before their departure they received a lot of training on the physics of eclipses and how to record different observations, points out Trivedi, a theoretical astrophysicist.

I encouraged them to build their own equipment, says Trivedi, whose days as an observational astronomer back at Caltech helped him teach the students about the various observational techniques. We used standard (high f-number) camera and (48 x zoom) video camera, but I asked them to try and mount on them other equipment such as grating, filters and polarisers and improvise their equipment. They had to import only two pieces of equipment, the transmission gratings and holographic polarisers.

The students found innovative ways to match their equipment to the filters, gratings and polarisers. Having arrived a full 48 hours before the eclipse day, they practised with their set-ups and carried out a complete rehearsal the day before. This showed that the elevation of the sun was a good and convenient 13-14{+o} at the scheduled eclipse time. An eclipse observation requires a great deal of planning and preparation and the importance of fully rehearsing the day before was impressed upon me by Nirupama Raghavan [ex-Director of the Nehru Planetarium, New Delhi], says Trivedi. The expedition was sponsored by Nirupama Raghavans son, Vivek Raghavan of Magma D.A., Inc. The exact observing site within Mohaniya was chosen for its isolation and clear view of the north-eastern horizon. At Mohaniya, totality began at 06-25-50 a.m. and lasted three minutes and 39 seconds, according to Trivedi.

The observations carried out by the students were mainly of two types: images and spectrum. They recorded direct, polarised and cross-polarised images of the eclipsed sun and were also able to capture the solar corona, a large prominence during the C2, chromosphere, the diamond ring effect and, most significantly, the flash spectrum. Flash spectrum refers to the abrupt changes in the spectrum in the emission-line spectrum of the suns chromosphere, which flashes out in the few seconds before the beginning and at the end of totality.

Slitless spectrographs, which the students obtained, show the flash spectrum as a series of thin crescents (as an enlargement of the picture does reveal), each marking the position of a prominent emission line from the chromosphere. Both polarised and unpolarised spectra and even second-order spectra were recorded, as was the coronal spectrum, which is visible for the entire duration of totality. The students carried out both still and video recordings for all these observations.

Light intensity variations, using a light dependent resistor (LDR) and a multimeter circuit, and temperature variations with time were also recorded at intervals of five seconds (though a part of it was apparently missed because of some mishap). Though the students did not see the shadow bands with their eyes, the specific video experiment that was done to capture them is being currently analysed to see if they were detected. At the time of totality, they also captured images of Mercury, Venus and the stars Sirius and Capella.

Almost all the scientific goals of the expedition were achieved, says Trivedi. A special highlight is the video recording of the suns corona as it abruptly appears around the sun. The students learnt a lot from this expedition and now have a different outlook on scientific research that is complementary to their classroom and laboratory activity. The hard work put in by the students really paid off, the professor says.

It was a nice trip and a great experience, the students say unanimously. Their achievement may not be professional, but given the various challenging and scientifically interesting observations that they have carried out with skill and innovation, they have probably done better than many other astronomy groups tracking the rare TSE over India.

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