Solar observatory in Rajasthan is situated at -

RPSC deleted this question in its final answer key, so no option is marked correct.

The four options are cities with different science facilities. Here is what each one hosts, according to the sources named below.

Udaipur hosts the Udaipur Solar Observatory (USO) of the Physical Research Laboratory (PRL), a unit of the Department of Space. ISRO's page on USO's Multi Application Solar Telescope says the observatory is situated on an island in the middle of Lake Fatehsagar.

Jaipur has the Jantar Mantar, a collection of 19 astronomical instruments built by Sawai Jai Singh II. Jodhpur hosts two remote sensing centres, one state and one central.

Ajmer is named in the Economic Review 2020-21's sentence on the regional offices of Rajasthan's Department of Science and Technology: "located at Ajmer (Headquarter Jaipur), Bikaner, Kota, Jodhpur and Udaipur".

The idea to keep: a solar observatory studies the Sun with telescopes; remote sensing centres study the Earth from satellite data.

Why the others are wrong

• (1)
  Udaipur — Udaipur hosts the Udaipur Solar Observatory of PRL. ISRO says it sits on an island in Lake Fatehsagar, where the surrounding water reduces heating of the surface layers, lowers air turbulence and improves image quality.

  ISRO also reports that USO's 50 cm Multi Application Solar Telescope (MAST) was made operational in 2015 to study solar activity, including its magnetic field.

• (2)
  Jaipur — Jaipur has the Jantar Mantar. Wikipedia's article (October 2021 revision) describes it as a collection of 19 astronomical instruments built by Sawai Jai Singh II, founder of Jaipur, and completed in 1734.

  Its instruments, which include stone sundials, allow astronomical positions to be observed with the naked eye. The article lists it as a UNESCO World Heritage site.

• (3)
  Ajmer — Ajmer is named in the Economic Review 2020-21's sentence on the regional offices of Rajasthan's Department of Science and Technology, printed as: "regional offices located at Ajmer (Headquarter Jaipur), Bikaner, Kota, Jodhpur and Udaipur."

  The department's own website (April 2021 copy) gives the same list as "Ajmer (H.Q. Jaipur), Bikaner, Kota, Jodhpur and Udaipur".

• (4)
  Jodhpur — Jodhpur hosts two remote sensing centres. The State Remote Sensing Application Centre (SRSAC), Jodhpur "is also working under" Rajasthan's Department of Science and Technology, in the words of the department's website (April 2021 copy).

  NRSC's website places ISRO's Regional Remote Sensing Centre, West at Kuri Bhagtasani Housing Board, Jodhpur. Both work with satellite data of the Earth.

A solar observatory studies the Sun. PRL's page on USO lists research on solar oscillations, magnetic and velocity anomalies in sunspots, the Sun's active-region magnetic fields, solar eruptive phenomena, coronal mass ejections and space weather.

Site matters for a solar telescope. ISRO explains that the lake around USO's telescopes decreases heating of surface layers and air turbulence, improving image quality and seeing.

PRL, according to ISRO, has campuses at Ahmedabad, Mt. Abu (Infrared Telescope), Udaipur (MAST) and Thaltej.

Key facts

• USO belongs to the Physical Research Laboratory (PRL), which ISRO describes as an autonomous unit of the Department of Space.
• ISRO: USO is situated on an island in the middle of Lake Fatehsagar, Udaipur.
• ISRO: USO's Multi Application Solar Telescope (MAST) has a 50 cm aperture and was made operational in 2015.
• PRL's photographic atlas of the solar chromosphere uses USO observations collected during 1976–1984.
• Jaipur's Jantar Mantar is a collection of 19 astronomical instruments built by Sawai Jai Singh II and completed in 1734 (Wikipedia).

Common traps

• Two kinds of observatory: Udaipur's USO observes the Sun through telescopes such as the 50 cm MAST, while Jaipur's Jantar Mantar is a set of instruments, completed in 1734, for observing astronomical positions with the naked eye.
• Remote sensing is not astronomy: Jodhpur's SRSAC and RRSC-West work with satellite data of the Earth.
• PRL's telescope campuses named by ISRO are Mt. Abu (Infrared Telescope) and Udaipur (MAST), apart from its Ahmedabad and Thaltej campuses.

UnlockIAS will link similar questions from RAS Pre 2018 here once that paper is published on this site.

• practice — not a real PYQ

  The Udaipur Solar Observatory is run by –

  • (a)Physical Research Laboratory, Ahmedabad
  • (b)Indian Institute of Remote Sensing
  • (c)National Remote Sensing Centre
  • (d)Department of Science and Technology, Rajasthan
  Answer(1) — ISRO and PRL describe USO as the Udaipur Solar Observatory of the Physical Research Laboratory, a unit of the Department of Space whose main campus is at Ahmedabad. Options (2) and (3) are remote sensing institutions, and option (4) runs the State Remote Sensing Application Centre at Jodhpur.
• practice — not a real PYQ

  The Multi Application Solar Telescope (MAST) at the Udaipur Solar Observatory has an aperture of –

  • (a)15 cm
  • (b)50 cm
  • (c)1 m
  • (d)2 m
  Answer(2) — ISRO describes MAST as an off-axis Gregorian-Coude telescope with a 50 cm aperture. Options (1), (3) and (4) are not the aperture ISRO gives.