Astronomy

The History Of Astronomy In Early 19th Century India

sun spots

A six-inch aperture equatorial telescopes was purchased in 1850 by the British in India. It marked an important milestone in the progress of building an observatory in India. It was used to observe double stars, Jupiter and Saturn and their satellites. The telescope was remodeled and installed in Kodaikanal in 1900. New object glasses were subsequently added to the telescope, which was used for taking a daily photograph of the sun. It is still in use as a Photoheliograph. In 1866, a new 8-inch equatorial telescope was erected on the roof of the astronomer’s residence. In 1931 the telescope was shifted to Kodaikanal, but was installed there only in 1954.

It is a remarkable coincidence that Max Planck (1858-1947) developed the quantum theory around 1900. The simple equation he proposed indicated that the frequency of light emitted by an excited atom, for example, was directly proportional to the energy decrease of the emitting atom.

The British used the Kodaikanal observatory for an earthly purpose too. The observations facilitated an accurate determination of its longitude, which was important to fit India into a world map. The observatory also provides the reference meridian for the survey of India maps. The Great Trigonometrical Survey of India began in Madras on April 10, 1802. It was continued for about 25 years under the dedicated supervision of Sir George Everest, whose name was later given to the highest Himalayan peak, discovered in 1856.

The survey work, however, did not dilute the main task of observing the sky. The then Director of the observatory, Norman Robert Pogson (1829-1891) discovered six variable stars and as many asteroids from 1861 to 1891. Pogson’s assistant, an Indian astronomer, Chintamani Ragoonathacharry (1838 – 1932), discovered a variable star, R. Reticuli in 1867. This is the first recorded astronomical discovery by an Indian in recent history. After Pogson’s death, the 8-inch telescope fell into disuse, until it was revived in 1960.

In the latter part of the 19th century, three solar eclipses brought several astronomers from aboard to India to observe the Sun. In an unpublished note, the late Manali Kallat Vainu Bappu (1972-1982), a distinguish astronomer, who became the director of the Kodaikanal observatory, noted that the eclipse studies laid the foundation of astrophysics and created the subject of solar physics in India . On August 18, 1868, the French astronomer, Janssen (1824- 1907) used spectroscopy for the first time to study the Sun. He discovered the gaseous nature of the solar prominence’s. The hydrogen emission lines seen in the prominence’s were so strong that Janssen reasoned that they could be seen without an eclipse. He was proved right the very next day, when he studied light from its very edge through a prism without the obscuring Moon.

sunrise next to building

The 1868 eclipse was best observed from Machilipatnam, now in Andhra Pradesh. Several foreign taems of astronomers participated in the observation. The government astronomer in Madras, Pogson found interesting details in the solar spectrum during the eclipse. The hydrogen lines emitted by the sun were confirmed.

The eclipse created a puzzle. There was an unexplained bright yellow line close to the line of sodium in the solar spectrum. It was not emitted by any known element at the time. The British team at Guntur and a French team south of Hyderabad observed the new line in the spectrum. Joseph Norman Lockyer (1836-1920) , attributed it to a new element in the Sun, to be known as helium , deriving from the Greek word ‘Helios’ for the sun . It was only after about three decades (1895), did William Ramsay (1852-1910) identify it in a laboratory experiment on a mineral!

Janssen was also the first to note the granular appearance of the Sun in areas free of sunspots. Lockyer too scored some firsts. He was the first to study the spectra of Sun-spots. He named the Sun’s outer layer, the chromosphere. .

In 1871 the total solar eclipse was observed from Ootacamund and Pundukottai in south India. Janssen reported the discovery of dark absorption lines in the coronal spectrum. Pogson observed another interesting feature of the Sun. In 1872, he studied the annular solar eclipse, when the moon covers the center of the Sun, but not its edges, leaving a ring of the Sun visible around its edges. He saw a flash from the outer region of the sun-the spectrum of the chromosphere. This is believed to be the first observation of a flash spectrum from the chromosphere during an annular eclipse. Pogson and his colleagues are also credited with the discovery of nine asteroids, besides several variable stars.

Pogson was a good observer of stars too. He pointed out the the average first magnitude star is just about 100 times as bright as the average sixth magnitude star. He suggested that this hundredfold increases as representing an exact 5 magnitude difference. The suggestion has since been accepted.

An expedition under Naegamvala observed the solar corona during the 1898 total solar eclipse. He studied the chromosphere and the corona. His observation was a landmark. It proved that an Indian astronomer could do sophisticated observation of celestial wonders along modern lines. Two other expeditions led by Evershed and Lockyer respectively, observed the solar eclipse along the path of totality from Ratnagiri to Schdol in Central India.

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