Science & Tech

Solar Observatory of Kodaikanal

  • For over a century, the Kodaikanal Solar Observatory (KoSO) has been observing the Sun.
  • For over a century, Kodaikanal Solar Observatory (KoSO) has been observing the Sun. KoSO has captured images of sunspots and recorded changes in the Sun’s behaviour.
  • Solar physicists at the Indian Institute of Astrophysics (IIA) and the Aryabhatta Research Institute of Observational Sciences (ARIES) have digitised 1.48 lakh images of the sun taken since 1904.

Kodaikanal Solar Observatory: A Brief History

  • KoSO is one of the world’s oldest solar observatories.
  • Norman Pogson, astronomer and Government Astronomer at the Madras Observatory, proposed photographing the Sun with a 20-inch telescope.
  • In 1786, a British East India Company official made a private effort to establish the Madras Observatory.
  • In 1893, the decision was made to build a solar observatory, and Kodaikanal in present-day Tamil Nadu was chosen for its high altitude and dust-free environment.
  • The Solar Physics Observatory, later renamed KoSO, first opened its doors on April 1, 1899.
  • The Bhavnagar Telescope, named after the Maharaja of Bhavnagar, was one of the more well-known instruments at KoSO during its early years.
  • Solar images were captured on photographic film or plate using a 15cm telescope.
  • Since 1911, photographic films and plates have been used to record solar magnetic plages and prominences.

Solar Observations, One Per Day: How Are They Made?

  • Every day since 1904, white light images of the Sun have been captured using a 6-inch telescope.
  • Sunspots on the Sun’s surface are visible in visible light images.
  • Every day at 8 a.m., one image is taken, as has been the case for over a century.
  • Each observation is accompanied by the corresponding date and time, which is important for later calibration.
  • These plates or films are delivered to the darkroom and developed the same day or the following day.
  • After developing the film, the date and time of observation are written on the plate and recorded in the logbook.
  • These plates or films are carefully stored in humidity-controlled rooms in an envelope with the handwritten date and time of observation.

Arrival of New Technology and the Digitization Process

  • All solar observations between 1904 and 2017 were recorded on photographic films and plates.
  • A new telescope outfitted with CCD cameras has taken over and has been observing the Sun since 2017.
  • Prof J C Bhattacharyya initiated the digitization of the records in 1984, and others continued the effort.
  • The scientific community was given access to digitised solar observations from 1921 to 2011.
  • Raw and calibrated data from 1904 to 2017 have been added, and the digitization process is nearly finished.
  • KoSO now has a digital repository of 1.48 lakh solar images totaling 10 terabytes of data.
  • There are 33,500 white-light images (showing sunspots), 45,000 Ca II K spectral line images (showing plages), and 70,000 H-alpha photographic plates (showing prominences).
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