The 3.6 metre Devasthal Optical Telescope, the largest optical telescope in India, is operated by which institute?

The correct answer is B, Pune in Maharashtra. The array stands at Khodad, near Narayangaon, about eighty kilometres north of Pune, on flat land chosen for its low level of man-made radio interference, and it is operated by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. A, Nainital, is the district that holds Devasthal, where the optical telescopes of ARIES are placed, so the two sites are often interchanged in options. C has no major radio array of this kind, although it hosts other scientific institutions. D is the home of the Vikram Sarabhai Space Centre, which builds launch vehicles and is not an observatory. Remember GMRT with metre wavelengths and with Maharashtra. The array works in the band of about 100 to 1,500 megahertz, where pulsars and hydrogen clouds are studied.

The correct answer is A, thirty dishes of forty-five metres each. Fourteen of them stand close together in a central square of about one kilometre, and the remaining sixteen are spread along three arms in a Y shape stretching some twenty-five kilometres, which gives the array both the sensitivity of a filled aperture and the resolution of a wide one. The dishes are built of a light wire mesh stretched over a frame of rope trusses, a design that made them cheap enough to build in India. B understates both numbers. C simply swaps the two figures, which is exactly the trap an examiner wants a hurried candidate to fall into. D matches no Indian facility at all. Fourteen dishes in the central square and sixteen on the three arms is the split worth carrying into the exam hall.

The correct answer is A, Hanle in Ladakh. The Indian Astronomical Observatory sits there at about 4,500 metres in a cold desert, one of the highest and driest observing sites in the world, where very little water vapour and almost no artificial light make the sky exceptionally clear and dark. The telescope is operated by remote command over a satellite link from the centre at Hosakote near Bengaluru, which saves observers the journey. B holds the infrared telescopes of the Physical Research Laboratory. C holds the 2.34 metre Vainu Bappu Telescope of the same institute that runs Hanle, which is why the two are confused. D is the site of the GMRT radio array and has no optical telescope. The same site also carries the high altitude gamma ray telescopes of the atomic energy establishment, which need equally clear air.

The correct answer is B, the Kodaikanal Solar Observatory in the Palani hills of Tamil Nadu, set up in 1899 when solar work was moved from the old Madras Observatory to a hill station with clearer air. It is now part of the Indian Institute of Astrophysics, and its digitised archive of daily photographs of the solar disc, sunspots and the chromosphere is among the longest continuous records of the Sun anywhere, which makes it valuable for the study of long solar cycles. A is a night-time optical observatory for stars and galaxies. C watches the Sun but at radio frequencies and was set up much later. D is an optical site of the twenty-first century with no solar programme of this kind. Its sunspot drawings and spectroheliograms are now used to reconstruct the solar activity of the past hundred years.

The correct answer is A, Kavalur in Tamil Nadu. In 1977 astronomers watched Uranus pass in front of a distant star from the observatory in the Javadi hills, and the dips in the star's light before and after the planet itself crossed showed that rings surround Uranus. The site later received the 2.34 metre telescope named after Vainu Bappu, who founded the observatory, and it belongs to the Indian Institute of Astrophysics. B is a solar observatory and could not have made such an observation. C was developed as an observing site only in the closing years of the twentieth century, two decades after the event. D hosts optical telescopes but had no part in this particular discovery. The method used, watching a star dim as a body passes in front of it, is called occultation.