Instrumentation
A 10-foot Solar Spar was acquired through the kind courtesy of Late Prof. R.G. Giovanelli from the CSIRO, Australia. This Spar was slightly modified. A new diffraction limited 15 cm aperture F/15 singlet objective lens, corrected for H-alpha was installed on the spar along with a Halle' H-alpha filter (HBW 0.5 A°), a 35mm time lapse camera, intervolometer and a servo controlled guider. The 20 mm diameter primary image is enlarged by a 'Schneider' positive relay lens to yield an image scale of 24 to 36 second of arc per mm. Thus on a 35 mm format about 8 x 6 arc minute region on the Sun could be photographed. Pictures could be taken at a maximum rate of 1 per second. On the same spar a multislit spectograph for taking spectra around H-alpha (~10A°), a solid state photometer and a TV camera are mounted.
The overview of the telescope is illustrated in linked Figure. The light beam from the objective O, is focused on the aperture stop A, which in turn is enlarged by the relay lens RL. With the help of the 50:50 cube beam splitter BS1 part of the light is diverted to the multislit Littrow spectrograph LS, and partly to the H-alpha filter. The multislit spectrograph consist of 12 slits separated by 1 mm on an aluminized glass plate, to give dispersion of 10A°/mm. A blocking filter NBF, of half band width of 8A° is placed before the camera, C2, to filter-out the over-lapping spectra formed by other slits. The multislit could be shifted in steps of 0.1mm, to scan and take H-alpha spectra over a 5 x 3 arc minute region on the Sun. This spectrograph is used to take spectra of active regions, prominences, solar flares and other activities. The light beam passing through the Halle' H-alpha filter is again divided in two directions by a cube beam splitter BS2- one to a 35mm time lapse camera for taking H-alpha filtergrams and other to a third beam splitter BS3. This beam splitter allows part of the H-alpha image to fall on a high resolution, low light sensitive TV camera and part on a solid state photometer (SSP), PM. The TV camera is used to monitor the solar images and SSP to observe the intensity variation of various solar phenomena. To obtain full disk white light pictures of the Sun, a 15cm aperture objective, a relay lens and a camera are also mounted on the side of the spar. A 30mm white light image is formed on a film for sunspot observations.
For full disk H-alpha observation, a Razdow 12.5cm aperture telescope, along with a Halle' H-alpha filter and time lapse camera have been acquired from the Space Environmental Services Centre of NOAA, Boulder.