The Indian Astronomical Observatory (IAO) is a high-altitude astronomy station located in Hanle, India and operated by the Indian Institute of Astrophysics. Situated in the Western Himalayas at an elevation of 4,500 meters (14,764 ft), the IAO is one of the world's highest located sites for optical, infrared and gamma-ray telescopes.^[1] It is currently the tenth (see List of highest astronomical observatories) highest optical telescope in the world. It is India's first dark-sky preserve.^[2]

Location

The Indian Astronomical Observatory stands on Mt. Saraswati, Digpa-ratsa Ri, Hanle in south-eastern Ladakh union territory of India.^[3] Accessing the observatory, located near the Chinese border (Line of Actual Control), requires a 250 km long ten-hour drive from Leh city, the headquarter of Leh district.^[4] Nyoma, 75 km northwest from Hanle, has an Indian military airbase.^[5]

History

In the late 1980s a committee chaired by B. V. Sreekantan recommended that a national large optical telescope be taken up as a priority project. The search for the site of the observatory was taken up in 1992 under the leadership of Arvind Bhatnagar. The scientists from the Indian Institute of Astrophysics found the site at Hanle.^[6]

The first light was seen by the Observatory 2-metre telescope on the midnight hour between 26 September and 27 September 2000.^[3]

The satellite link between the Centre for Research and Education in Science and Technology (CREST), Bangalore and Hanle was inaugurated by the then Jammu and Kashmir Chief Minister Farooq Abdullah on 2 June 2001. The Observatory was dedicated to the nation on 29 August 2001.^[7]

Dark-sky preserve and astrotourism

Hanle Dark-sky preserve

In September 2022, it became India's first dark-sky preserve.^[2] The Hanle site is deemed to be excellent for visible, infrared and submillimeter observations throughout the year.^[4] Specifically the observation conditions yield about 255 spectroscopic nights per year, approximately 190 photometric nights per year and an annual rain plus snow precipitation of less than 10 cm. In addition, there are low ambient temperatures, low humidity, low concentration of atmospheric aerosols, low atmospheric water vapour, dark nights and low pollution.^[3] The preserve extends to the 6 hamlets of Hanle revenue village - Bhok, Dhado, Punguk, Khuldo, Naga and Tibetan Refugee habitation within 1073 sq km Changthang Wildlife Sanctuary in Changthang plateau. North, south, east and west four extremities of the preserve are between a distance of 19.6 km to 22 km from the observatory.^[8]

The darkness of night sky is classified on the bortle scale from 1 ("excellent", i.e., extremely dark) to 9 ("Inner-city sky", i.e., partially dark). The dark sky is important for the conservation of nocturnal animals and ecology. To minimize light pollution and to ensure dark skies, Hanle preserve has many restrictions such as lights must be indoors only, mandatory light-blocking curtains on windows and doors, only warm yellow lights (wavelength does not travel far) on streets, no high beam headlights on vehicles, no vehicle movement at night, etc.^[9]

To avoid the altitude sickness, the extra tourist must acclimatize for a day or two at Hanle (at 4500 m elevation) or Leh.^[9]

Astrotourism

There are many astrotourism locations in India ranging from Ladakh, Himachal Pradesh, Uttarakhand, South India to Andaman Nicobar Islands. Among these Uttarakhand has highest number of public and private night sky observatories, such as Aryabhatta Research Institute of Observational Sciences (ARIES) in Devasthal in Nainital district. Uttrakhand government is also setting up observatories at Abbott Mount in Champawat district, Pithoragarh, Kausani, Jadhang (or Jadung, under the Vibrant Villages programme), and Takula (in Nainital). In Uttarakhand, a startup named Starscapes also has private astrotourism observatories at Bhimtal, Kausani, and astrovillage Benital in Chamoli district.^[9]

There are more than 100 planetariums in India. Nehru Planetarium is based in five locations Mumbai, New Delhi, Pune and Bangalore and Prayagraj. The Kalpana Chawla Planetarium in Jyotisar in Kurukshetra in Haryana.^[10]

In 2023, India had more than 15 private observatories for astrotourism that came up in last five years, many of which have their observatories in multiple locations. Astrostays, a startup, organises astrotourism trips to Pangong in Ladakh. In Karnataka, the Association of Bangalore Amateur Astronomers (ABAA) meets every Sunday at Banglore Nehru Planetarium and Bangalore Astronomical Society (BAS) organizers regular astro tours to outskirts of city and to remote locations of India. Starvoirs, Chennai based startup, as private observatories in nine places across the country, including Rameshwaram, Chidambaram, Kodanad, Andaman Islands, Nagaland, etc.^[9]

The astrotourism potential in India is underutilised and underdeveloped. There are numerous places in India that could be developed, designated and preserved as the dark sky preserves, for example, Madikeri in Coorg is surrounded by coffee plantations and natural forests rates 3 three (rural sky) on the Bortle scale. Just like the Project Tiger has immensely helped conservation of tiger, ecology and reduction of carbon footprint, the issue of conservation of dark skies could help conservation of ecology and nocturnal animals, but there is a very low awareness of this. There is it a no nationwide plan to systematically develop more dark sky areas with the mandatory lighting restrictions. The designation of dark sky preserve by the International Dark-Sky Association (IDA) is a 3 year process, which involves identifying dark sky areas, preparing a development and conservation plan, and submitting a proposal to IDA for the designation. India urgently needs such a nationwide program, but as of 2023 there is none.^[9]

Facilities

The Observatory has several active telescopes. These are the 2.01 meter optical-infrared Himalayan Chandra Telescope (HCT), GROWTH-India telescope, Cassegrain telescope, and a High Altitude Gamma Ray Telescope (HAGAR). The HCT is remotely operated from Bangalore from the Centre for Research and Education in Science and Technology (CREST) using a dedicated satellite link.

Himalayan Chandra Telescope (HCT)

The Himalayan Chandra Telescope is a 2.01 meters (6.5 feet) diameter optical-infrared telescope named after India-born Nobel laureate Subrahmanyam Chandrasekhar.^[4] It contains a modified Ritchey-Chretien system with a primary mirror made of ULE ceramic which is designed to withstand low temperatures it experiences.^[11] The telescope was manufactured by Electo-Optical System Technologies Inc. at Tucson, Arizona, USA. The telescope is mounted with 3 science instruments called Himalaya Faint Object Spectrograph (HFOSC), the near-IR imager and the optical CCD imager.^[4][12] The telescope is remotely operated via an INSAT-3B satellite link which allows operation even in sub-zero temperatures in winter.^[11]

GROWTH-India Telescope

The GROWTH-India telescope is a 0.7 meter wide-field optical telescope that had first light in 2018.^[13] It is the country's first fully robotic research telescope.^[14] It was set up as a part of the international GROWTH program,^[15] and has been widely used for time domain astronomy. The telescope is operated jointly by IIT Bombay and the Indian Institute of Astrophysics.

Punjabi University, Patiala (Punjab) 24 inch Cassegrain telescope Observatory

In 1980s, 24 inch Cassegrain telescope was installed at 90 feet height in a huge dome of the observatory in the Punjabi University, Patiala campus. Department of Physics, Punjabi University, Patiala is the only one department in the northern India, which have this unique facility.^{[citation needed]}

IIA-Washington University Cassegrain telescope

Since 2011, the Indian Institute of Astrophysics (IIA) collaborates with the McDonnell Center for the Space Sciences of Washington University in St. Louis to operate two 0.5 meters Cassegrain telescopes to monitor active galactic nuclei. One of the observatories is established in Hanle.^[4] The facilities 180 degrees apart in longitude are together to be called the Antipodal Transient Observatory (ATO).^[16]

High Altitude Gamma Ray Telescope

The High Altitude Gamma Ray Telescope (HAGAR) is an atmospheric Cerenkov experiment with 7 telescopes setup in 2008.^[17] Each telescope has 7 mirrors with a total area of 4.4 square meters. The telescopes are deployed on the periphery of a circle of radius 50 meters with one telescope at the center. Each telescope has alt-azimuth mounting.^[18] A Himalayan Gamma Ray Observatory (HiGRO) was set up at Hanle in collaboration with Tata Institute of Fundamental Research, Mumbai and Bhabha Atomic Research Centre, Mumbai.

Major Atmospheric Cerenkov Experiment Telescope (MACE) was set up here in December 2012.^[19] The Experiment has a 21-meter collector which can collect gamma rays from space.^[19] The facility is a result of initiative led by Bhabha Atomic Research Centre in collaboration with Tata Institute of Fundamental Research, Indian Institute of Astrophysics, Bangalore and Saha Institute of Nuclear Physics Kolkata. The facility cost in 2011 was Rs. 400 million.^[19] As of 2011, it was the first and only such facility in the eastern hemisphere.^[19] The telescope was fabricated by the Electronics Corporation of India and was installed at the IAO in June 2014.^[20] This Telescope became the second largest gamma ray telescope in the world and the world's largest telescope at the highest altitude.

Center for Research and Education in Science and Technology

The Center for Research and Education in Science and Technology (CREST) is situated 35 km to the northeast of Bangalore near Hoskote town. The Center houses the control room for the remote operations of the 2m Himalayan Chandra Telescope (HCT) at the Indian Astronomical Observatory, Hanle, and the HCT data archive. The operations are controlled using a remote satellite link.^[21]