by Gurbir Singh
The transit was observed from the terraces of Fort St. George in Madras by William Hirst shortly after sunrise on 6 June 1761. Hirst recorded what came to be known as the black drop effect where the sharp circular edge of the silhouette of Venus appeared distorted as it entered and exited (ingress and egress) of the disc of the Sun. In Hirst’s words “at the total immersion, the planet, instead of appearing truly circular, resembled more the form of a bergamot pear”[91], an effect similar to the distortion of the circular shape of the Sun as it sets over the horizon. The black drop effect limited the precision of the timing of the transit.
In the 19th century, the first transit of Venus occurred soon after the technique of spectroscopy had demonstrated its potential as a potent tool for science. During the transit, astronomers quantitatively measured, for the first time, the atmospheric properties of another world. A thick atmosphere was detected on Venus, which helped explain the black drop effect, limiting the precision of the timing measurements for the beginning and end of the transit. Observations with modern telescope suggest that the black drop effect was not entirely due to Venus’s atmosphere but a result of instrumental effects, Earth’s and the Sun’s atmosphere.[92] By the late 19th century, astronomers had been observing the heavens with telescopes for over 150 years. Telescopes had improved optically with larger lenses and mirrors; enhanced engineering for gears and drives for telescopes resulted in larger, brighter and clearer images. Developments in clocks also provided increased reliability and precision of astronomical observations.
Figure 2‑5 Transit of Venus 8th June 2012. Had photography been available the 1761 transit would have looked similar. Credit Author
The ‘‘worldwide transit enterprise of 1874 was thoroughly shaped by national political ideologies”[93] converging with technological advances. France, Germany, the USSR and the US organised expeditions with the goal of measuring the Earth-Sun distance. In 1874, astronomers were able to determine an approximate value for the Earth-Sun distance (also known as the astronomical unit), and thereby the scale of the solar system, by measuring with high precision from several geographically distant locations on Earth the time that Venus entered and exited (ingress and egress) the disc of the Sun during the transit. Following the transit of 1874, there was another in 1882, which was not visible from India. Data of both transits collected by astronomers from Italy, France, the USSR, UK, US, Germany and South America were correlated and analysed. The Earth-Sun distance was refined to 92.95 million miles ± 0.19 million miles (149.59 million km ± 0.31 million km).
The Director of the Madras Observatory, Norman Pogson, was taken ill in June 1891 and died a few weeks later from cancer. One of his last actions was to recommend by letter to the Chief Secretary of the India Office that Charles Michie Smith (1854–1922) be his successor. Norman Lockyer did not have high regard for Smith and preferred Kavasji Dadabhai Naegamvala (1857–1938) instead.[94] Naegamvala had set up the Takhtasingji Observatory in Poona (now Pune) with a 20-inch (50.8 cm) telescope, the largest in India at the time. The India Office overruled Lockyer and Pogson’s recommendation was selected.
The Madras Observatory remained the primary astronomical observatory in India for over a century. Its focus was not just on the routine recording of astronomical observations but also in the pursuit of scientific knowledge. However, attempts to upgrade and develop the instruments and facilities at the Madras Observatory were unfruitful. In 1899, all astronomical activity was moved to the Kodaikanal Observatory, and the Madras Observatory was re-tasked to undertake meteorological observations.[95] The work of astronomical observatories in India was designed to mitigate risks, predominantly of bad weather during long journeys at sea. This would be critical for an Empire with ambitions to grow.
Kodaikanal Observatory
Three solar eclipses (in 1868, 1871 and 1872), three transits of Mercury (5 November 1868, 7 November 1881 and May 1891) and one transit of Venus (9 December 1874), with this series of rare and spectacular celestial phenomena in the late 19th century, the interest in studying the Sun peaked. All of these, by chance, were visible from India. Lunar eclipses (shadow of the Earth on the Moon) can be seen from anywhere on Earth where the Moon is above the horizon at the time of eclipse and can last for around four hours. A total solar eclipse (shadow of the Moon on the Earth) is much rarer, lasts only for a few minutes and is visible from small areas on the Earth.
The Moon is 400 times smaller than the Sun, but because it is 400 times closer to the Earth, they both appear to be about the same size in the sky. This is responsible for the spectacular beauty of a total solar eclipse, the Moon in front of the Sun surrounded by the Sun’s atmosphere – the corona. The Moon is much smaller than the Earth and so is its shadow. When it falls on the Earth, the shadow of the Moon has a diameter of only about 93.20 miles (150 km). During a total solar eclipse, this shadow races across the Earth’s surface at around 0.62 miles/s (1 km/s) over a ground track approximately 9,320.57 miles (15,000 km) long.[96]Although the total duration of a solar eclipse is over a few hours, totality (that is, the period when the Moon completely obscures the Sun) experienced by a stationary observer on the ground lasts only a few (typically five) minutes.
With most of the celestial events of the late 19th century visible from India, the idea of a solar observatory in India attracted considerable interest and support. Key scientific discoveries, all centred on the Sun, seemed to further validate the intellectual case for building a solar observatory in India, and the Kodaikanal Observatory was sanctioned. The Kodaikanal Observatory initiated the systematic study of solar physics in India.
Figure 2‑6 Kodaikanal Observatory. 1908. Credit Unknown Artist
The construction of the Kodaikanal Observatory commenced at the end of April 1895, and it became operational in 1900. The 89-acre site, 1.24 miles (2 km) above sea level, is in southern India on the Western Ghats equidistant from Madurai and Coimbatore. The Observatory was the product of a decade-long struggle by Charles Michie Smith, to build an observatory on a mountaintop. In a letter to the Under Secretary of State for India dated 17 August 1883, the then Astronomer Royal William Henry Mahoney Christie (1845–1922) stated “I am not prepared to endorse Mr Pogson’s remarks as to the enormous improvement in defining power necessarily resulting from a great elevation.”[97] In the absence of Pogson, Smith defended this argument, and the mountaintop site was eventually approved. Today, all professional astronomical observatories are placed on mountain tops to minimise the atmosphere through which the faint light from distant stars must travel.[98]
The Evershed Effect
Smith was a dedicated astronomer and an industrious administrator without whom Kodaikanal Observatory probably would not have been established. Although he did not make any major scientific contributions, his chief assistant and later successor, John Evershed (1864–1956), did. Evershed arrived at Kodaikanal in 1907. An accomplished amateur astronomer specialising in spectroscopy, he had held the responsibility of Director of the Solar Spectroscopy section of the British Astronomical Association.[99] In 1907, he observed Comet Daniel and, in 1910, Comet Halley using the observatory’s 6-inch (15.24 cm) aperture telescope. He recorded spectra and identified nitrogen and carbon in the nuclei of both comets. In the tail of Halley’s Comet, he identified carbon monoxide.
Evershed was experienced in observing the Sun photographically and spectroscopically. He had made regular observations of sunspots over many years. On the particularly clear morning of 5 January 1909, Evershed, assisted by his wife Mary, captured from Kodaikanal the spectra two large sunspots. Upon carefully examining the absorption lines, he noted “the spectra revealed a curious twist in the lines crossing the spots which I at once thought must indicate a rotation of gases.”[100] He had recorded the evidence of gas emanating from the centre of the sunspots and being pushed radially outwards by magnetic fields associated with the sunspot. This phenomenon had been predicted earlier, but Evershed was the first to capture evidence. The effect has s
ince been known as the Evershed Effect.
The actual value of the pressure pushing the gases was not known until Meghnad Saha (1893–1956) published his work on thermal ionisation in 1920, which helped to quantify the pressure that prevailed on the surface of the Sun.[101] Interestingly, in the following year, Evershed invited Saha to come and work at Kodaikanal, but Saha declined.[102]
In 1911, Smith retired, and after a short trip back to Scotland, he returned to India, which he made his final home. He died in 1922 and is buried in India close to the observatory.
Other Observatories
A by-product of the GTS and the astronomical techniques it relied on was a series of astronomical observatories established in India during the 19th century, in Lucknow (1831–49), Trivandrum (1837–52), Dehradun (1878–1925), Calcutta (1879) and Poona (1888–1912).[103] During the colonial period, leaders of all significant scientific institutions in India, including astronomical observatories, were vetted and approved in Britain by organisations, such as the Royal Society, British Astronomical Association and the British Association for the Advancement of Science. In most cases, the funding also came from the Britain, but there were a few exceptions.
In 1831, the Nawab of Oudh set up an observatory in Lucknow, and in keeping with the traditions, he requested a British director to lead it. Major James Dowling Herbert (1791-1833), a GTS officer, was Lucknow Observatory’s first director. The observatory was well equipped, and high-quality observations were made, but none were ever published. When its subsequent director Richard Wilcox (1802–1848) died in 1848, the observatory fell into disuse. Lucknow was the centre of some of the fiercest fighting during the 1857 revolt. When Lieutenant-General James Francis Tennant (1829–1915) of the Bengal Engineers recaptured Lucknow, he discovered the building intact, but the contents had been ransacked.[104]
The motivation for the Trivandrum Observatory came from British scientists. The British monarch provided the funding but with key local support. Swathi Thirunal Rama Vermah (1813–1846), Maharaja of Travancore, “entered warmly into the project” and appointed his astronomer to manage the observatory.[105] Its location was determined in part for the same reason that Thumba was selected a century later as India’s first rocket launch site, the close vicinity to the magnetic equator. Observations taken from a latitude of 8° 30' 35” N were considered likely to yield valuable results owing to its proximity to the equator.[106]
The observatory had several instruments, including a telescope with a 5-inch (12.7 cm) aperture. Although marginally more effective in producing scientific observations due to its location close to the magnetic equator, the Trivandrum Observatory, like the Lucknow Observatory, failed to produce significant astronomical observations during its active period. A decade and a half after its inception, the instruments were in a poor state, and John Broun (1817–1879), the Observatory Director appointed in 1851, changed the role of the observatory. It was re-tasked to record observations in magnetism and meteorology rather than astronomy.
Figure 2‑7 Halley's Comet photographed by John Evershed from Kodaikanal 1910. Credit Indian Institute of Astrophysics
The observation of the solar eclipses of 1868, 1871 and 1872 and the transit of Venus in 1874 helped observational astronomy get a foothold in India.[107] It also supported the case for establishing a more permanent facility in India to monitor the Sun regularly, where it was more reliably accessible than the cloudy British skies. Norman Lockyer convinced the Secretary of State for India, Lord Salisbury (1830–1903), that a telescope already in India for the 1874 transit of Venus should be deployed in a more permanent facility to routinely observe the Sun.
Figure 2‑8 Eugène Lafont (1837–1908). Credit Grentidez
Dehradun Observatory in the foothills of the Himalayas was approved in September 1877, and it started its systematic observations of the Sun in early 1878. As part of the Survey of India established in 1767 (of which later the GTS was a part), photographs of the Sun’s disc were taken regularly and sent to the UK on a weekly basis between 1878 and 1925.[108] The function of the Dehradun Observatory was routine solar observation rather than scientific investigations of the type undertaken at the Kodaikanal Observatory established in 1900.
A science enthusiast and Belgian Jesuit priest, Father Eugène Lafont (1837–1908) helped establish an observatory in Calcutta, which survives to this day. Lafont was a professor of science at St. Xavier’s College. His rooftop observatory was initially designed to gather meteorological data, and it became operational in 1867. The transit of Venus brought many Europeans to India. One was Professor Pietro Tacchini (1838–1905) of Palermo Observatory in Italy. Jointly, they observed the transit, Lafont optically and Tacchini spectroscopically, from Madhapur north of Calcutta, a site Lafont had identified as suitable.[109] After the transit, Tacchini encouraged Lafont to set up a solar observatory and conduct spectroscopic observations of the Sun to complement his work in Italy.[110]
By 1879, Lafont had raised funds and rebuilt his college rooftop observatory into what became the St. Xavier’s College Observatory in Calcutta. It was equipped with a 7-inch (17.78 cm) equatorially mounted telescope housed in a large dome supported by two spectroscopes, one for use with a telescope and the other for visual observations. As part of its role as a teaching facility, the observatory was primarily used to observe sunspots and prominences. As such, it was India’s first observatory dedicated to the scientific investigation of the Sun.[111]
Lafont’s contribution was more than just his rooftop observatory. He helped nurture the scientific renaissance of the late 19th century in India by holding popular public talks on scientific subjects. Among his students at St. Xavier’s College was Jagadish Chandra Bose (1858–1937), who studied physics. Bose demonstrated radio waves in 1895 in Calcutta prior to Marconi’s demonstration of transatlantic radio communication in 1901. When controversy arose over who invented the radio, Lafont championed recognition for his former student. Lafont also helped to establish the Indian Association for the Cultivation of Science (IACS), where the Nobel Laureate C.V. Raman conducted his first laboratory experiments. The observatory Lafont set up in 1867 was renovated in 2014 and renamed the Fr. Eugène Lafont Observatory.[112]
Another Indian pioneer in observational astronomy was Gode Venkata Juggarow (1817–1856). He had trained at the Madras Observatory for four years with Taylor. In 1840, he built his private observatory at Daba Gardens in Visakhapatnam on the east coast. He made his observations using a 4.8-inch (12.192 cm) telescope. Juggarow published several scientific papers in the Madras Journal of Literature and Science based on his own observations of Jupiter and Lunar occultations.[113] Following his death in 1856, first, his son-in-law and then his daughter managed the observatory before it was handed over to the Madras government in 1894. Papers published by Juggarow Observatory included measurements of the mass of Jupiter, observations of three solar eclipses (18 August 1868, 12 December 1871 and 17 May 1882), all partials from Daba Gardens and transits of Mercury (5 November 1868, 7 November 1881 and 10 May 1891) and significant work on comets, including Comet Pons-Brooks on 31 January 1884.
The first observatory funded and operated entirely by Indians was the Takhtasingji Observatory founded in Poona in 1882. Initially, Maharaja Takhtasingji of Bhavnagar donated Rs. 5,000 matched by an equivalent sum by the Bombay (now Mumbai) government to establish a spectroscopy laboratory at the University of Bombay (now University of Mumbai). The switch from a laboratory in the University of Bombay to an observatory in the College of Science in Poona was probably driven by an academically gifted Naegamvala, whom Lockyer later wanted to succeed Pogson as the Director of the Madras Observatory. He had strong connections in Bombay and Poona. Naegamvala had secured his Bachelor of Arts in 1878 and Master of Arts in physics and chemistry from Bombay by the age of 21, and then, he served as the professor of astrophysics in the College of Science in Poona.
Figure 2‑9 Bhavnagar Telescope in Ladakh 1984. Credit Indian Institute Astrophysic
s
Having secured the funds in 1882, Naegamvala travelled to Europe and North America to understand the latest technology in astronomical instrumentation and techniques. He visited observatories in Germany, Italy and Spain. He spent time with Norman Lockyer in London, from whom he acquired training in the use of modern equipment and observational techniques, especially spectroscopy and photography.[114] Naegamvala called on the assistance of Astronomer Royal Sir Christie to help him compile a list of equipment for his observatory. In July 1884, Naegamvala visited the premier designer and builder of telescopes, Howard Grub (1844 -1931), in Dublin and placed an order for a 16.5-inch (41.91 cm) reflector telescope. It was the largest telescope in India at the time and remained so for several decades. Having placed the order, he returned to India. Four years later, the Takhtasingji Observatory containing the Bhavnagar telescope was in operation with Naegamvala as its director.