| Abstract : | Observations of electromagnetic radiation from astronomical sources can be observed from the ground in
two major windows that are not significantly absorbed in the atmosphere: (1) Optical window that
extends a bit on both sides of visible electromagnetic spectrum and sometime called UVOIR; (2)
microwave and longer wavelengths generally referred as “radio”. Very high energy gamma-ray photons
incident upon earth interact with Earth’s atmosphere to produce a shower of elementary particles that
travel faster than the speed of light in the medium and thus produce Cerenkov radiation in the ultraviolet
and blue region. The latter photons can be observed with optical facilities and the incident VHE gamma
ray photons can be inferred. In this talk I describe significant milestones in the development of
astronomical facilities in India utilizing the optical window as outlined below.
During the early part of 20th century, Kodaikanal Solar Observatory was the only world class facility in
India operating in the optical region. The observatory is significantly upgraded in the 1960s, Udaipur
Solar Observatory was established a decade later and has seen a major addition in the recent decade. The
solar astronomy community is planning a new facility that will be competitive globally in the future.
Optical astronomy got a significant boost with 1-m class telescopes around 1970, 2-m class telescopes
since mid 1980s and a 3.6 m telescope during the last decade. India is currently participating as a partner
in the international Thirty Meter Telescope project and wishes to build a 10-m class facility on Indian
soil.
Activities towards VHE gamma-ray observations also began in 1960s and several experiments were
performed culminating in the HAGAR wavefront sensing array in the first decade of the century and 21-
m MACE facility installed recently. |
