Kodaikanal Observatory

Full Disc Imaging
  • Photoheliograph
  • A 15 cm aperture English mounted refractor by Lerebour and Secretan, acquired in 1850 and remodelled by Grubb in 1898 to serve as a photoheliograph, is in use since the beginning of this century to obtain 20 cm white light pictures of the Sun on a daily basis, sky permitting.

  • Spectroheliograph
  • Twin spectroheliographs giving 6 cm diameter full disc photographs of the Sun in Calcium K and hydrogen alpha lines are in regular use. A 46 cm diameter Foucault siderostat feeds light to a 30 cm aperture f/22, Cooke triplet lens. The two prism K spectroheliographs were acquired in 1904 and the H alpha grating spectroheliograph was operational in 1911. Since 1912, prominant pictures over the full limb are also being obtained in K by blocking the solar disc. These observations and the white light pictures are obtained around 200 days a year.

  • K-filtergrams
  • Light from the 46 cm siderostat is diverted to a 15 cm Zeiss achromat objective which provides an f/15 beam and a 2 cm image. A prefilter and a daystar Ca K narrow band filter are used together with a Photometrix 1k x 1k CCD to record the K filtergram. Regular observations have started in 1996-97. Besides synoptic observations, temporal sequences are being obtained on days of good to excellent seeing.

Last updated on: May 5, 2017