Kodaikanal in Tamil means ‘summer, a mirage’. Apparently, the name indicates that there is no summer in Kodaikanal, which is a picturesque hill station near Madurai, one of the hottest cities in South India. Kodai, as it is familiarly known, is the hill station in the Pazhani hills, located at 10 degree 13’ (minutes) 50” (seconds) North of the equator. From the nearest railway station, a road journey to the top of the hills takes less than two hours, En route, one can buy the world famous jasmine flower and a wide variety of fruits.
A solar observatory is located at the highest point in Kodai viz., 2343 meters above mean sea level. One is struck by the sheer weight of the equipment hauled up before the days when the roads were laid to the top. The trouble was worth it as the pioneers realized the reason for establishing a solar observatory at that point. It is simply the atmosphere at Kodai, which is stable with low air turbulence. The atmospheric condition is ideal for obtaining an undisturbed image of the Sun through a telescope, though by the afternoon, clouds set in. In the plains, air turbulence would make an image of the Sun wobble. Even in Kodai, the telescope has a dome to reduce the atmospheric heating.
Some distance away from the blaring TV commercials in the town center at Kodai, one can regain the quiet serenity of the hills, and enjoy the aroma of some of the lush green trees that have escaped the axe of development. As one watches the brilliant blue sky, the date with the sun seems to be too good to last longer. You run for cover as n all-enveloping mist gives way to a cloud burst. As the rain peters out, the red Sun behind the hills plays hide and seek with the red and white roses overlooking the lake. The sky turns a bit white for a white for a while before twilight. One could hardly imagine a more picturesque presentation of Raleigh scattering!
Public Visiting Timings
The general public can visit the observatory for a tour of the facility from 10am to 12 pm and 2pm to 4 pm on weekdays. As one enters the precincts of the Observatory, one is overwhelmed by a sense of history. The Observatory has been functioning for well over a century. Few research institutions in India can match this record in continuity. It was in 1898 that the British East India Company shifted its observatory in Nungambakkam, Madras to Kodai. The first Director of the Observatory, Rev. Fr. Michie Smith who moved the equipment from Madras was an astronomer.
He refurbished a 15 cm aperture telescope, which had been brought to Madras in 1850, and installed it at Kodai. It was used as a photo heliograph to get 20 cm white light pictures of the Sun on a daily basis, sky permitting. A two-prism heliograph, acquired in 1904, recorded calcium lines in the solar spectrum. A grating spectrograph, operational from 1911, captured the H-alpha hydrogen line. The lines indicate the presences of hydrogen and calcium in the Sun. Since 1912, pictures over the full limb have also disc. The spectral and optical (white light) imagery could be obtained on about 200 days in a year.
The Observatory has a unique record: it has photographed the Sun daily for over 100 years without a break from 1900! Only Mount Wilson Observatory and the Meudon observatory in France may have a somewhat similar collection. The uninterrupted data on the solar phenomena have become highly topical and relevant in view of the importance given to the impact of the Sun on the Earth, triggered by the International Geophysical Year (2007-2009).
One of the most remarkable discoveries made from Kodaikanal relates to a better understanding of the physical properties of Sunspots and the evolution of solar activity John Evershed (1864-1956) began life as an amateur astronomer. He was involved in the discovery of ultraviolet spectrum of prominence’s during the total eclipse in 1898. He joined the observatory in 1905 and because its Director in 1911. He designed and made several instruments for the observatory. He started a programme of photographing the prominences of the Sun in hydrogen light. He investigated the spectra of Sunspots and observed small shifts in their spectrum. An important discovery he made in 1909 is named after him. Called the Evershed Effect, it refers to the radial outflow of the constituent gases in Sunspots.
The discovery was based on the observations made in Kodai. He also confirmed these observations from a temporary field station in Kashmir. Evershed constructed a measuring device to study the minute shifts in the solar magnetic field. He focused the spectrograph across a Sunspot and found a displacement of spectral lines, which indicated outward radial motion. Later, he found that this motion was in the reverse direction for gases in the higher chromosphere. This is the first time that a relationship was seen between magnetism and moving matter. It is remarkable that hardly was there any addition to his finding in the next 50 years. It is noteworthy that there are still ongoing worldwide studies on the Evershed Effect.
Evershed built a spectroheliograph and put it to good use to photograph the spectra of different regions of the Sun on every clear day in a narrow band centered around the ionized calcium line in the spectrum, which throws light on the upper layers of the chromosphere. Evershed later added another spectroheliograph to this instrument using a grating to take the picture of the Sun in the H-alpha line.
Evershed was fascinated by the large widths of the absorption lines, especially that of hydrogen. He observed the sharp absorption of hydrogen and calcium lines in the spectrum and identified their source in the Sun and interstellar gas clouds. He measured the spectra of the solar limb with that of the center of the Sun to study the solar rotation.
In 1909, Evershed discovered many small displacement of lines equivalent to velocities of the order of a few tenths of a kilometer per second in the chromosphere. For another 50 years, astronomers concentrated on these phenomena and found this type of wave phenomena in the solar photosphere and chromosphere. Evershed also discovered oxygen lines in the emission from the chromosphere even when there was no eclipse. He found variations of the hydrogen lines and used them in studying the solar atmosphere.
After Evershed retired in 1923, solar observations at Kodaikanal slowly became routine. The instruments used by him are rather simple and they are in good shape even today. Both he and his wife simply fell in love with the place. Lady Evershed planted rare plants and trees near the Observatory and some of them are now quite tall and big.
Today at the Observatory, one can have in less than a second the entire image of the Sun in the desired wavelength as well as in both ionized calcium and hydrogen alpha lines. These lines are widely used to study the Sun’s chromosphere. The lines respond to the magnetic fields of the Sun and the solar activity, which causes constant variability in the solar irradiance. As the Sun is the largest source of energy to Earth, any change in the solar output would affect the energy balance of the Earth’s surface.
The data on the calcium line, detected by a CCD camera, are stored in a computer since 2001. By using a narrow band filter, the entire picture of the Sun either in H-alpha or in Calcium-K line can be taken in seconds.
Prior to 1960, the Observatory had 15 cm white light Photoheliograph to study the Sun and spectroheliographs to monitor the solar activity, besides a 20-cm refractor telescope to study the stars. In 1961, a solar tower telescope was added to the observatory. It was in fact the result of one man’s enthusiasm. Anil Kumar Das (1945-1960), the fifth Director of the Observatory, took a keen interest in planning the facility. Meanwhile, Vainu Bappu succeeded Das as the Director of the Observatory in 1960. Bappu initiated a programme to study the Sun as a star.