Indian Astronomical Observatory

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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]


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]


In the late 1980s a committee chaired by Prof. 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 Prof. 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 Dr. Farooq Abdullah on 2 June 2001. The Observatory was dedicated to the nation on 29 August 2001.[7]

Observation: Dark-sky preserve[edit]

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 Observatory has several active telescopes. These are the 2.01 meter optical-infrared Himalayan Chandra Telescope (HCT), a High Altitude Gamma Ray Telescope (HAGAR), and . 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)[edit]

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.[8] 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][9] The telescope is remotely operated via an INSAT-3B satellite link which allows operation even in sub-zero temperatures in winter.[8]

High Energy Gamma Ray Telescope (HAGAR), Hanle

GROWTH-India Telescope[edit]

The GROWTH-India telescope is a 0.7 meter wide-field optical telescope that had first light in 2018.[10] It is the country's first fully robotic research telescope.[11] It was set up as a part of the international GROWTH program,[12] and has been widely used for time domain astronomy. The telescope is operated jointly by IIT Bombay and the Indian Institute of Astrophysics.

IIA-Washington University Cassegrain telescope[edit]

Since 2011, the Indian Institute of Astrophysics (IIA) collaborates with the McDonnell Center for the Space Sciences of Washington University in St. Louis in USA 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).[13]

High Altitude Gamma Ray Telescope[edit]

The High Altitude Gamma Ray Telescope (HAGAR) is an atmospheric Cerenkov experiment with 7 telescopes setup in 2008.[14] 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.[15] 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.[16] The Experiment has a 21-meter collector which can collect gamma rays from space.[16] 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.[16] As of 2011, it was the first and only such facility in the eastern hemisphere.[16] The telescope was fabricated by the Electronics Corporation of India and was installed at the IAO in June 2014.[17] 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[edit]

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.[18]

See also[edit]

Tourism and infrastructure


  1. ^ "Indian Astronomical Observatory, Hanle". Indian Institute of Astrophysics. 20 November 2020. Retrieved 13 November 2022.
  2. ^ a b All you need to know about India's first dark sky reserve in Ladakh, Business Standard, Karthik Jerome, 9 September 2022.
  3. ^ a b c News, Dec 25, 2000, Vol. 79 No. 12 Current Science, Indian Academy of Sciences
  4. ^ a b c d e Pallava Bagla (7 January 2002) "India Unveils World's Highest Observatory", National Geographic News, Retrieved 21 January 2011
  5. ^ "Eye on India, China raises Tibet military command rank | Central Tibetan Administration". Retrieved 1 October 2016.
  6. ^ Rajan, Mohan Sundara. "Telescopes in India". National Book Trust, India, 2009, p. 132
  7. ^ About IAO, IAO website. accessed on 20 January 2011.
  8. ^ a b Ravi Sharma (Volume 18 - Issue 20, 29 Sep - 12 Oct 2001), "A stellar acquisition"[Usurped!], Frontline; Retrieved on 25 January 2011
  9. ^ IAO Telescope Accessed on 21 January 2011
  10. ^ "GROWTH-India - First Light!". Retrieved 7 October 2020.
  11. ^ Sharma, Dinesh C. "India's first robotic telescope opens its eyes to the universe". @businessline. Retrieved 7 October 2020.
  12. ^ "GROWTH Observatories". Retrieved 7 October 2020.
  13. ^ Antipodal Transient Observatory. Archived 8 November 2016 at the Wayback Machine Accessed on 20 January 2011
  14. ^ Staff Reporter (13 December 2009) "Plan to establish Indian Neutrino observatory", The Hindu, Retrieved on 21 January 2011
  15. ^ Hagar Telescope Accessed on 21 January 2011
  16. ^ a b c d Sunderarajan, P (17 June 2011). "Gamma ray telescope getting ready at Hanle". The Hindu. Retrieved 17 June 2011.
  17. ^ MACE telescope ready to be shifted to Hanle, Ladakh from Hyderabad | Hyderabad News - Times of India
  18. ^ CREST Accessed on 21 January 2011

External links[edit]