‘World class’ optical telescope – India’s largest – to be activated near Nainital

Update: This article was written before the telescope was activated yesterday. Here’s the PIB announcement.

India’s largest ground-based optical telescope, in Devasthal in Uttarakhand, is set to be switched on on March 30 by the Prime Ministers of India and Belgium from Brussels, during Narendra Modi’s day-long visit to the country. The telescope is the product of an Indo-Belgian collaboration, assisted by the Russian Academy of Sciences, that was kicked off in 2007. It is going to be operated by the Aryabhatta Research Institute of Observational Sciences (ARIES), an autonomous research body under the Department of Science and Technology.

The instrument is part of a widening foray into observational research in astronomy that India has undertaken since the 1960s, and bolstered with the successful launch of its first multi-wavelength satellite (ASTROSAT) in September 2015. And apart from the merits it will accord Indian astronomy, the Devasthal optical telescope will also be Asia’s largest ground-based optical telescope, succeeding the Vainu Bappu Observatory in Kavalur, Tamil Nadu.

A scan of the sketch of the 3.6-m optical telescope. Credit: ARIES
A scan of the sketch of the 3.6-m optical telescope. Credit: ARIES

Its defining feature will be a 3.6-metre-wide primary mirror, which will collect light from its field of view and focus it onto a 0.9-m secondary mirror, which in turn will divert it into various detectors for analysis. This arrangement, called the Ritchey-Chrétien design, is also what ASTROSAT employs – but with a 30-cm-wide primary mirror. In fact, by contrast, the mirrors and six instruments of ASTROSAT all weigh 1,500 kg while the Devasthal telescope’s primary mirror alone weighs 4,000 kg.

A better comparison would be the Hubble space telescope. It manages to capture the stunning cosmic panoramas it does with a primary mirror that’s 2.4 m wide. However, Hubble’s clarity is much better because it is situated in space, where Earth’s atmosphere can’t interfere with what it sees.

Nonetheless, the Devasthal telescope is located in a relatively advantageous position for itself – atop a peak 2.5 km high, 50 km west of Nainital. A policy review published in June 2007 notes that the location was chosen following “extensive surveys in the central Himalayas” from 1980 to 2001. These surveys check for local temperature and humidity variations, the amount of atmospheric blurring and the availability of dark nights (meeting some rigorous conditions) for observations. As the author of the paper writes, “The site … has a unique advantage of the geographical location conducive for astronomical observations of those optical transient and variable sources which require 24 h continuous observations and can not be observed from [the] east, in Australia, or [the] west, in La Palma, due to day light.”

From this perch, the telescope will be able to log the physical and chemical properties of stars and star clusters; high-energy radiation emanating from sources like blackholes; and the formation and properties of exoplanets. The data will be analysed using three attendant detectors:

  • High-resolution Spectrograph, developed by the Indian Institute of Astrophysics, Bengaluru
  • Near Infrared Imaging Camera, developed by the Tata Institute of Fundamental Research, Mumbai
  • Low-resolution Spectroscopic Camera

“India has collaborated with a Belgian company called AMOS to produce this [telescope], which is the first of its kind in the whole of Asia,” said Vikas Swarup, spokesperson of the Ministry of External Affairs, in a statement. AMOS, an acronym for Advanced Mechanical and Optical Systems, was contracted in 2007 to build and install the mirrors.

When Modi and Michel complete the so-called ‘technical activation’ to turn the Devasthal instrument on, it will join a cluster of scopes at the Indian astronomical research community’s disposal to continue surveying the skies. Some of these other scopes are the Giant Metre-wave Radio Telescope, Pune; Multi Application Solar Telescope, Udaipur; MACE gamma-ray telescope, Hanle; Indian Astronomical Observatory, Leh; Pachmarhi Array of Cherenkov Telescopes, Pachmarhi; and the Ooty Radio Telescope, Udhagamandalam.

In fact, over the last few years, the Indian research community has positioned itself as an active player in international Big Astronomy. In 2009, it pitched to host a third advanced gravitational-waves observatory, following the installation of two in the US, and received governmental approval for it in February 2016. Second: in December 2014, India decided to become a full partner with the Thirty Meter Telescope (TMT) collaboration, a bid to construct an optical telescope with a primary mirror 30 metres wide. After facing resistance from the people living around the venerated mountain Mauna Kea, in Hawaii, atop which it was set to be built, there are talks of setting it up in Hanle. Third: in January 2015, the central government gave the go-ahead to build a neutrino observatory (INO) in Theni, Tamil Nadu. This project has since stalled for want of various state-level environmental clearances.

All three projects are at the cutting edge of modern astronomy, incorporating techniques that have originated in this decade, techniques that take a marked break from the conventions in use since the days of Galileo. That Modi has okayed the gravitational waves observatory is worth celebrating – but the choices various officials will make concerning the INO and the TMT are still far from clear.

The Wire
March 30, 2016