Indian Astronomical Observatory | Where the stars must not twinkle

Clean skies, high altitude and complete darkness are vital for India’s cutting-edge astronomical observatory in Ladakh’s Hanle village. Jacob Koshy reports on the challenges in having it declared an International Dark Sky Reserve, and the efforts to make residents stakeholders in the process

October 08, 2022 12:40 am | Updated 10:10 am IST

A view of the Milky Way galaxy behind the Indian  Astronomical Observatory at Hanle in Ladakh.

A view of the Milky Way galaxy behind the Indian Astronomical Observatory at Hanle in Ladakh. | Photo Credit: R.V. Moorthy

Srinivasa Ramanujan was ‘discovered’ twice in the 20th century. The first was when English mathematician G.H. Hardy ‘discovered’ the genius mathematician in 1914; and the second was when Indian astronomers in India, led by R. Rajamohan, discovered an asteroid that was later named 4130 Ramanujan. It was the first time in 104 years that asteroids were discovered from India. Their instrument, the 45-cm Schmidt telescope, was housed on the Javadi hills in Kavalur, Tamil Nadu.

This spot is today the Vainu Bappu Observatory and is run by the Indian Institute of Astrophysics (IIA), Bengaluru, and is among India's foremost observatories. It was chosen in the 1960s because it was an impressive 750 metres above sea level, located amid a forest and offered fairly unobstructed vistas of the night sky.

Read | Can the Dark Sky Reserve at Hanle be a gamechanger for stargazing in India?

But this wasn’t ideal. Kavalur’s geography put it in the path of both monsoonal clouds, during June-September and the returning, or northeast, monsoon in November, forcing the observatory to often shut down for months. Rainclouds absorb starlight and radiation from cosmic objects, preventing them from being caught on the telescopes of cameras. So IIA scientists began their search in the early 1980s for a place least affected by the monsoon.

To be able to detect stars or traces of cosmic phenomena, such as supernovae or nebulae from light years away, astronomers must be able to catch the faintest slivers of their radiation that often lie outside the range of visible light. Such radiation is, however, easily absorbed by water vapour and so it helps to have a telescope high above ground where the atmosphere is drier. “A dry, high-altitude desert is in many ways the ideal location,” says Annapurni Subramaniam, Director of the IIA. “Such terrain is difficult and quite inaccessible. We commissioned several expeditions and teams to different parts of the Himalayas and finally Hanle, Ladakh was chosen.”

In the high ranges of Ladakh

A largely smooth double-lane highway from Leh, the capital of Ladakh, to Hanle cuts through a valley scooped out of the mountains of the Ladakh range and the teal-coloured Indus. Army units and border check-posts punctuate the landscape that opens out into the Changthang Wildlife Sanctuary, where you can spot the occasional herd of the Tibetan wild ass and swarms of leaf warblers. As the road ascends, a smattering of hamlets, surrounded by pasture land, comes into view with herds of Changthangi sheep, the source of pashmina wool.

Situated at 14,000 ft above sea level and a little over 250 km southeast of Leh, Hanle is a village of about 320 houses and a population of about 1,500, according to Paljor Therchin, the sarpanch of Hanle.

Against the backdrop of a blue sky flecked with cottony clouds, two huge metallic capsules — one higher than the other — incongruously rise out of the hills. Next to them, satellite dishes, like ushers, point to the sky. From here, a tarred road spirals down about 900 ft to flat land where makeshift cabins and a small building serve as ancillaries to a giant, parabolic dish that is a complex of a thousand mirrors bathed white in sunlight, resting on criss-crossing steel frames of red and blue. Men, some perched, some dangling on the beams, weave out of the meshes of this honeycomb structure.

Facing this are what look like seven concrete cannons, one in the centre and six surrounding it. Each has seven mirrors that together resemble a robot-contingent of photographers training their apertures at some uncertain blink-and-you-will-miss cosmic event.

This entire set-up, laid out on the mountain called Digpa-Ratsa Ri, aka Mt Saraswati, comprises the Indian Astronomical Observatory (IAO). The multicoloured dish is the Major Atmospheric Cherenkov Experiment Telescope (MACE) built by a consortium of the Bhabha Atomic Research Centre, the Tata Institute of Fundamental Research, the Electronics Corporation of India Ltd. and the IIA. The dish, with a diameter of 21 m, is the second largest of its kind in the world and the only one at such an elevation. Its goal is to detect Cherenkov radiation from space.

This is a special kind of light from gamma rays, or the most energetic sources of radiation, that can result from dying stars or several galactic events. The seven-telescope contingent, called HAGAR (High Altitude Gamma Ray), also looks at Cherenkov radiation, although at a lower range of energies. The metallic capsule, the highest of the observatories, is the Himalayan Chandra Telescope (HCT), the oldest and active since 2000. An optical-infrared telescope with a 2-metre lens is designed to detect light from the visible range of the electromagnetic spectrum as well as that just below it, or the infra-red spectrum. The second capsule, situated slightly lower than the HCT, is the GROWTH-India telescope, a 70-cm telescope made by IIA and the Indian Institute of Technology, Mumbai that is equipped to track cosmic events that unfurl over time, such as afterglows of a gamma ray burst or tracking the path of asteroids. Because of the wide span of frequencies covered collectively, the IAO provides multiple vantage points to observe a range of cosmic phenomena and investigate the mysteries of the universe. Telescopes with small diameters generally can track a greater swath of sky but those with larger diameters can peer deeper when trained towards desired locations.

The Indian Astronomical Observatory at Hanle village in Ladakh.

The Indian Astronomical Observatory at Hanle village in Ladakh. | Photo Credit: R.V. Moorthy

The flip-side of Hanle’s seclusion, making it ideal for astronomy, is the weather and climate. The altitude means that atmospheric oxygen is low, making one prone to mountain sickness.

Among the recommended paraphernalia on a trip to Hanle are cans of oxygen cylinders. The desiccated air that helps the telescope catch ephemeral interstellar light translates to sub-zero winters for at least six months of the year. The summer months from April to September have cold, windy nights, and with no access to the electric grid, the eager stargazer must brave runny noses and chills.

The IAO telescopes, however, can be controlled remotely via a satellite link. Whatever the weather, astronomers at the IIA’s Centre for Research and Education in Science and Technology (CREST), about 35 km from Bengaluru, can manoeuvre the HCT to face their desired spot of sky. The other instruments too are equipped to be remotely controlled. While the HCT is manned 24/7, those on site are required only for maintenance and not for using the telescopes. Researchers who want a shot at using the instruments must apply, in fact compete, for observation time made available in quarterly slots; the applications are scrutinised by scientific committees.

“The available time is over-subscribed three times. Every astronomer, even when they have their own telescopes, applies to use these because of the quality of sky and the large number of viewable nights that the telescopes offer. It is their bread and butter,” says Subramaniam.

In recent years, these telescopes have helped gain a better understanding of a system of Earth-sized planets orbiting the TRAPPIST-1 star, about 40 light years away from Earth, as well as gravitational waves that resulted from the collision of neutron stars from a billion years ago, she adds.

The play of light and dark 

While these sophisticated instruments and their images are manipulated by scientists, all that novice visitors have to do to realise they are in a special place is look up at the night sky. At least 300 nights a year, the clouds would have been swept away, and the vista looks as if some invisible, giant being had kicked up a sandstorm of stars. Contrary to the thumb rule that ‘the lights that twinkle are stars, those that don’t are planets’, the sky is studded with unblinking lights.

Twinkling stars imply starlight is being bounced around by atmospheric gases, dust and water vapour, and therefore obscuring to us on land its origins. At Hanle, the thinner air and the elevation means starlight is relatively unimpeded until it descends into the lower, more polluted stretches below.

“Here’s Jupiter, that bright point straight ahead. From here trace a straight line to the right till you see that dim star-like point. That’s Saturn,” Dorje Angchuk gesticulates to craned necks. “You don’t need your phone’s flashlight to navigate here. Close your eyes, clear out the artificial light, absorb the darkness, and open them. You’ll see everything.” As chief engineer at IIA, Angchuk, a native of Leh and the person in-charge of the HCT systems, has made countless trips to Hanle in the last quarter century and been closely involved in the installation of IAO telescopes.

In the last couple of years, he has curated an avidly-followed Twitter stream of night-sky photographs of Hanle. Over the last several months, particularly since Ladakh was marked out as a distinct Union Territory from Jammu and Kashmir, he has been in the thick of a project that will shape the future of Hanle.

Dark Sky Reserve 

“Light is the enemy,” says Pawan Kotwal, Principal Secretary in the Ladakh Administration, referring to the phenomenon of light pollution in which artificial light from cities and home electrification have obscured the natural night sky. Recent studies show that clouds, the biggest reflectors of sunlight, scatter artificial light from ground-based sources, amplifying light pollution.

For astronomy, a discipline that hinges on the wisps of light, artificial sources of light are contaminants. Thubstan Rinchen, the officer in charge of MACE, said in an IIA-commissioned documentary that light from, say, the high beam of a vehicle at night would flood the sensors of the telescope. Separating this light from that collected as part of experiments is a cumbersome process and results in loss of scientific data.

Hanle, as it currently stands, is largely shrouded in darkness. Disconnected from the electric grid, solar panels and a diesel generator are the only sources of electricity. Hanle only gets electricity from 7 p.m. to 11 p.m. The freezing months, says Padma Lazo, who runs a homestay here, can see temperatures dip to minus 40°C, though cookstoves and dung provide heat. “We don’t need electricity all the time but better jobs and schools for our children would be welcome.”

Ladakh’s recent Union Territory status, a government eager to expand economic opportunities via tourism and the Indian Army expanding its infrastructure development, lighting to bolster its defence at the India-China border which is not far away — all these are challenges in keeping light from seeping into Hanle.

To strike a balance, the Ladakh government along with the IIA and India’s Scientific Ministries is laying the groundwork to have Hanle declared as an International Dark Sky Reserve by the International Dark-Sky Association. Since 1988, the U.S.-based non-profit has been advocating the cause of minimising light pollution and certifies places where night skies are least polluted as International Dark Sky Reserves or sanctuaries.

“The average tourist visits for high roads, exotic landscape, and the Pangong Lake. Hanle is already in a wildlife sanctuary and developing it as such a reserve would encourage a newer kind of tourism, or astro-tourism,” says Kotwal. “The most important condition, however, is that it must have the support of the local community.”

In the weeks ahead, amateur and professional astronomers have been roped in by the IIA and the local government to give talks on constellations to villagers. As many as 18 telescopes will be set up in village clusters, and homestay owners trained in elementary astronomy to guide astro-tourists. Villagers will also be given dark curtains to minimise outgoing light from residences. Already, at night time, vehicles are restricted from pointing their beams upwards, and roads will be installed with light delineators.

Having been promised electrification in two years and funds from the government to improve their homes to homestays, residents of the village say they would be happy to comply with light restrictions. “That’s not a problem for us. However, more than residential lights, it’s the light from Army bases that are actually stronger. That should be managed too,” says Therchin, who is also a religious head at a nearby monastery.

Kotwal and Angchuk say Commanding Officers of the units have “readily agreed to comply”.

“We have a long-standing relationship with the community and they were involved in construction of the existing facilities,” says Subramaniam. So far, the relative height of the HCT had protected its observations from light pollution, and while the region’s development is inevitable, setting out guidelines and restrictions on light would ensure that both astro-tourism and the immaculate skies can coexist, she adds.

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