In late September, 40 amateur astronomers and photographers from all over India converged on the tiny hamlet of Hanle, in Ladakh. We were at the Hanle Dark Sky Reserve. This is one of very few spots in India where ambient light doesn't overwhelm the night sky.
Now that is something to celebrate. Therefore, the annual Hanle Dark Sky Party, run by the Indian Astronomical Observatory. Four nights out in the cold, looking up at the stars. Even merely thinking about it got my pulse racing, and I don't think it was just Hanle's altitude of 14,000 feet. After all, this is why I had applied to join the Party in the first place. And here we were, in a vast open area, among Indian Astronomical Observatory's various telescopes, looking up at the fantastic sky, photographing, observing, soaking it all in.
Early one night, I set my camera to take multiple shots of the Milky Way, with a small Indian Astronomical Observatory telescope in the foreground to give it some perspective. Then I made my way through the inky darkness to the telescope. When I walked up its stairs, I heard a gasp. I was startled too, and quickly identified myself. It was Nasrath from Bangalore, settled there for the night. She was using her binoculars to scan Sagittarius, home to some well-known deep sky objects like nebulae, and thus always a fine target. So I got out my binoculars too, and followed her directions to good effect. Over a pleasant hour or so, we found the Lagoon and Triffid Nebulae and some more. Then we swivelled right - westward - to locate two globular clusters in the nearby constellation Ophiuchus, M10 and M12.
Again, the ease with which she directed me: "Start at Antares, then go up a little to that not-so-bright star, then a little further in the same direction, you should see M10 and M12 in the same field of view." About then, Ritik from Bombay joined us, and he navigated the sky with casual aplomb. "The Andromeda Galaxy?" he asked. "Check the Great Square in Pegasus. From the star in that corner, come to that second bright star, then make a right-angle turn to the right, go past two more stars, and you'll see Andromeda at two o'clock."
Sure enough, I did. Two o'clock it was. How do Nasrath and Ritik - how do all these folks here - know these objects so well?
There was Ayush from Gurgaon, set up not far from me so I walked over for a chat while we waited for dark. He had a slender telescope pointing north, fitted with electronics so that it could track the motion of our Earth. You need that for any serious observation and photography of deep sky objects like nebulae or galaxies. And sure enough, he got some beautiful shots of the Triangulum Galaxy and the North American Nebula. Ayush knows his equipment and the skies well - I'm not sure which better, but both like the back of his hands. I asked what I hoped were informed questions about both; he answered with what I can only describe as a gracious expertise. No condescension, just an obvious desire to share his knowledge.
Elsewhere, Nayan had brought his 16-inch telescope - a nearly human-sized mélange of poles and mirrors. "Let's take a look at the Andromeda Galaxy!" I heard him say as I walked up, and within seconds he had swung the instrument around, lined it up using its smaller "finder" scope, and ... "there, take a look!" and yes, there was our galactic neighbour, like a beautiful cloud of white with a prominent dark region that is its "dust lane".
A little later: "Shall we try Saturn?" And again, within seconds, there was Saturn, its rings just a thin line, tiny moons off to the side, brilliant and gorgeous to make you gasp. And Jupiter with stripes and its own moon like a small pea, and the Butterfly and Ptolemy Clusters in Scorpius, and the Triangulum Galaxy ... I envied Nayan, as I did so many others on this field, his easy familiarity with the night sky.
Not just with the night sky, either. Let me explain.
Now the 40 of us were spread across several homestays in Hanle. There's a plan, even a story, there.
A crucial part of the thinking behind the Hanle Dark Sky Reserve is that it must take Hanle's residents along in the attempt to preserve the precious dark sky. To that end, the folks at the Indian Astronomical Observatory have come up with a slew of measures. They've given the residents heavy curtains for their windows, campaigned against cars using headlights, enlisted several of the youth as "Astronomy Ambassadors", given them training and eight-inch telescopes so they can show off the sky to friends and visitors. These Ambassadors conduct astro-tourism shows for tourists and earn money by charging for those sessions. And then there are the myriad homestays. They are a boon for the steady flow of tourists who come here for the stars, as also for the residents themselves, able to earn something from that flow and feel like they have a stake in the Reserve.
Of the 40, twelve of us were in Lhamo homestay, basic and clean, which is all we wanted. Our fourth day in Hanle, September 22, was the autumn equinox. Sourabh, a PhD student from Pune, announced he was going to take the opportunity to measure the Earth's circumference.
Not at night, like most of our other Hanle Dark Sky Party activities, but during the day.
An ambitious task? But it's not as if Sourabh was planning to set off on a trek around the globe, tape measure in hand. No, he would replicate a famous experiment attributed to the ancient Greek mathematician Eratosthenes. On the summer solstice over 2,200 years ago, Eratosthenes measured the length of shadows cast by the sun in two cities - Alexandria and Syene (modern day Aswan). With Syene sitting almost exactly on the Tropic of Cancer, the sun was directly overhead that solstice day, and cast no shadow. But in Alexandria, a pole did cast a shadow. Using the angle made by the pole and its shadow, and the distance between Alexandria and Syene, Eratosthenes estimated the Earth's circumference. His 40,000 km figure is remarkably close to 40,075 km, the accepted number today for the planet's circumference at its equator.
Following those ancient Greek footsteps in Lhamo's courtyard bathed in sharp mid-day sun, Sourabh found a convenient pole casting a shadow. But he erected a pencil on his notebook and used its shadow as well. On the equinox, the sun is directly above the equator, and when it is at its zenith - noon, of course - in the sky, it will cast no shadows there. Elsewhere, like Lhamo, that zenith is when shadows are shortest. So that's what Sourabh wanted to nail down, using a series of red marks for the pencil, and a series of pebbles for the pole. The shortest shadow gave him the angle he needed, and given Hanle's latitude of 32.79° North, he knew we were about 3,640 km from the equator.
The calculated circumference? Using the pencil, 40,852 km. Using the pole: 39,483 km. The spirit of Eratosthenes, alive in Hanle. We Lhamo denizens whooped and cheered.
Back among the Indian Astronomical Observatory telescopes late that night, I set up my camera to record the rise of the Pleiades in a timelapse. For a break while it shot the sky, I wandered into the MACE (Major Atmospheric Cherenkov Experiment) telescope's control room. In a scene reminiscent of my student days, there were several engineers at work, monitoring data streaming in from MACE. A few of us visitors too, getting warm. Udayan, a student of management accounting in Bangalore, and I got chatting with one of the engineers, Keshva.
Keshva is an engineer from Himachal Pradesh and has been here at Hanle for several years. By his own admission, he was not particularly interested in astronomy when he got here - this was a job like any other. But over the years, he has learned and now enjoys the science, which explains the knowledge and passion that's evident as he speaks about his work.
Now I'm trained in engineering too, and so I felt like I understood a fair amount, if not all, of what he was saying. But the surprise was Udayan. From a couple of previous conversations, from watching him out on the field, I knew astronomy is a serious hobby. This night, he was on far more equal terms with Keshva than I was: discussing optics, data, electronics, and much more of all the technology that underpins modern astronomy. "I live and breathe astronomy, 24x7", he said at one point. Had I not known who these men were, had I stumbled on them conversing as they were, I would have assumed they were both astronomers. Later, I quietly suggested to Udayan - why not give up the accounting and take to astronomy? Was that over the top? His enigmatic smile at least hinted otherwise.
Back at my camera, I spent a while reviewing what I had captured.
One image has that small Indian Astronomical Observatory telescope on the left. Against its railing stands a little figure, pointing at the glorious spectacle above. That's me, that's the Milky Way. The spirit of four cold Hanle nights, in one image.
Tiny me, the unimaginably vast Milky Way. I feel the adrenaline.
These photos were taken at the Hanle Dark Sky Reserve Star Party 2025. The Star Party was organised by Indian Institute of Astrophysics, Department of Wildlife, Union Territory of Ladakh, and the Bhabha Atomic Research Centre. The Hanle Dark Sky Reserve is a joint venture between the Indian Institute of Astrophysics, the Union Territory of Ladakh, the Ladakh Autonomous Hill Development Council, Leh, and the local communities.
Dilip D'Souza is a writer based in Mumbai. His latest book is Roadwalker: A Few Miles on the Bharat Jodo Yatra.