It was 1982 and Liu Yan, an astronomer at the Purple Mountain Observatory in Nanjing, was at his desk responding to a letter about a mysterious light that had briefly appeared in the night sky over China. To his right was a stack of almost 200 letters, all about the same incident.

According to witnesses, on June 18, a “bright star” had suddenly appeared at about 10 p.m. just above the north horizon and then exploded, creating a dazzling white cluster that formed into a vast halo. Gradually, the light faded, and by 10:50 p.m. it had completely disappeared.

Hundreds of thousands of people reported seeing the phenomenon, from Heilongjiang province in the northeast to Jiangsu province along the eastern coast, and speculation was rife as to what had occurred. Was it the northern lights? A precursor to an earthquake? Aliens?

Based on his analysis of the eyewitness accounts, Liu had arrived at a more straightforward conclusion. “The strange celestial phenomenon was likely caused by a man-made spacecraft,” he wrote. “As the craft flew at an altitude of more than 1,000 kilometers, it revolved and simultaneously emitted solid and gas particles, creating a luminous mist of light with a ‘bright star’ at the center. When the craft stopped emitting particles, the revolving vapor dispersed outward, creating a white halo.”

He signed the letter, as he always does, “Purple Mountain Observatory Correspondence Department,” handed it over to be typed and mimeographed, and then went to collect a bunch of envelopes.

The 2021 movie “Journey to the West,” in which a journalist travels to a remote Chinese village to find evidence of aliens, brought back for many people memories of China’s UFO craze in the 1980s. Back then, the Purple Mountain Observatory would receive huge stacks of letters every time there was a strange celestial event, and Liu was generally the person tasked with replying. He would read and analyze every reported sighting, and he estimates he wrote at least 2,000 letters in response.

Liu turns 80 this year and has been retired for almost two decades, but he’s just as serious about his astronomy work. In a recent interview in the observatory’s conference room, he pulled from his backpack several binders stuffed with letters and other materials on celestial events across the country. He also maintains a keen memory for dates and details when it comes to specific UFO sightings.

In the 1980s, as Chinese society was opening up and things were in a state of flux, Liu’s letters demonstrated the power of science in breaking through the shackles of ignorance at a time when people were beginning to explore the unknown.

Shedding light on UFOs

Born in Haimen, Jiangsu province, Liu moved to Shanghai with his parents when he was 6 years old. He became interested in astronomy during middle school when he borrowed a copy of Young Astronomer magazine from a classmate. After that, every month he would spend his pocket money to buy Amateur Astronomer, and he and his classmate would visit People’s Square to look at the moon and spot constellations using a rudimentary telescope they made by fitting a lens into a cardboard tube.

It became Liu’s dream to be an astronomer, and in 1960 he was admitted to study in the astronomy department at Nanjing University. After graduation, he started working at the Purple Mountain Observatory, but the approaching Cultural Revolution saw astronomical research in China grind to a halt. Looking back at this period, Liu says he can’t recall taking part in any major scientific projects, except the observation of three solar eclipses.

However, his career reached a pivotal moment in 1981 when he was taken by his colleague Wang Sichao to meet with a group of students from Wuhan University who represented the China UFO Research Association. The organization was one of about 50 that sprang up nationwide in the wake of “UFOs: A Mystery Puzzling the World,” a People’s Daily article published in November 1978 that fueled wide public interest in the concept of extraterrestrial objects.

It was during this meeting with students that Liu developed an interest in the so-called July 24 Incident, his analysis of which began his journey from an expert on solar radio emissions to an all-around authority on unidentified flying objects, a field of study that some of his peers would over the years dismiss as “nonsense work.”

On July 24, 1981, at about 10:40 p.m., millions of people across China’s western provinces of Gansu, Sichuan, and Yunnan witnessed a spectacular bright spiral in the night sky that spun while slowly flying east to west.

Newspapers at the time reported that astronomers believed the special celestial event was caused by meteoroids from a Cassiopeia meteor shower approaching Earth. However, many experts disagreed.

Encouraged by his colleagues, Liu undertook a detailed analysis of the incident. After scouring eyewitness reports, he was able to determine that the celestial object on July 24 was likely a man-made aircraft flying at an altitude of about 650 kilometers. (By comparison, the International Space Station orbits Earth at an altitude of 420 kilometers.) Liu published his findings in Amateur Astronomer, marking his first article on UFOs.

The years that followed saw frequent sightings of halo- and spiral-shaped objects in the night sky over north China, generating a steady stream of letters to the Purple Mountain Observatory. In view of Liu’s response to the July 24 Incident, the observatory subsequently passed on any similar correspondence from the public to him.

“In the first couple of weeks after an incident, we’d receive lots of letters — scores, sometimes hundreds. By compiling all the information, it was possible to figure out the location of the object,” Liu says.

In theory, as long as you have observations of the apparent position and size of a UFO from more than two different locations, it is possible to calculate its true distance and size, as well as its average speed. “Ideally you want more than three data points, then the cross-referencing is more accurate,” he adds.

When responding to a letter about a UFO phenomenon, Liu’s explanation would usually fall into one of two categories: man-made aircraft or meteors. He also would add: “This is not an extraterrestrial ‘flying saucer,’ nor an omen of a coming disaster or a supernatural phenomenon. Please do not be alarmed. We shouldn’t believe old superstitions or rumors that are spread among the masses. Rather, we should inform them of scientific knowledge.”

Ignorance versus reason

During the interview at the observatory, Liu paused to point out a Song dynasty stone tablet engraved with a star chart. He joked that Nanjing taxi drivers are better than him at talking about stars, as they will tell stories and sometimes add lively details. “This is the North Star,” he said, pointing while mimicking the tone of a local cabbie. “If you rub this star, you’ll get promoted and be rich.” On the stone tablet, the spot with the North Star has been rubbed so many times that a small indentation has formed and the surface has become shiny.

It’s a stark example of how superstition can distract from science. Liu says he encountered many things in the 1980s and 1990s that had a significant impact on society but by today’s standards would be considered unthinkable.

One famous example was in 1994 when the media in China and overseas reported that a “flying saucer” had landed on Phoenix Mountain at a forest farm in Wuchang, Heilongjiang province. Meng Zhaoguo, one of the farm workers, even claimed he had been abducted by aliens.

Liu’s first reaction was that the reports were far-fetched, and when his university classmate Bian Yulin, a popular science writer, asked if he would write an article on the incident, Liu immediately agreed. He gathered all the reports he could find and pored over them for two months. His conclusion, which was serialized across three issues of Science and Technology Daily in January 1995, laid out the logical flaws in the various accounts.

At the end of his findings, he wrote, “I am of the belief that if the bizarre incident on Phoenix Mountain was not intentionally exaggerated or fabricated, then it can only have been a hallucination or delusion.”

It was by no means an isolated case. In 1988, Liu received a lengthy letter from a young man in Zhangye, Gansu, who claimed to have seen a flying saucer at about midnight on April 10, 1985. He said the object had fired a beam of white light at him, causing him to lose consciousness. He had then been taken by two little green men into their spacecraft.

“I had a lot of suspicions and there were too many signs of fabrication, so I returned the report to the young man,” Liu recalls.

He says the surge in such stories in the late 1980s resulted from UFO research in China taking a “wrong turn.” In 1988, for example, the China UFO Research Association accepted an invitation to become part of the All-China Qigong Science Research Association, an umbrella organization for the research and practice of qigong, an ancient healing practice that some say promotes pseudoscience. After that, some of its meetings to discuss UFOs included performances from qigong practitioners and people who claimed to have psychic powers.

“Some said they had the ability to speak cosmic languages, would do cosmic dances, and even said they could summon flying saucers with their minds,” Liu says with a laugh. After the 1990s, he said he became more cautious about attending UFO-related meetings.

“I’ve always believed that it requires modern scientific inquiry and results to study the mystery of UFOs, generally trying to discuss and explain them using natural or artificial phenomena in accordance with the laws of physics,” Liu says. “If there’s not enough observational data or there are other doubts, it can be put to one side for later analysis when new reports appear, or when multiple cases can be combined, to identify common patterns or causes.”

In search of truth

Since peaking in the 1980s and ’90s, UFO research in China has largely gone quiet. “No one has written to us to report a sighting in years,” says Zhang Yang, director of the Science Education Department at the Purple Mountain Observatory. Even on social media and internet forums, there are fewer reports about major UFO incidents.

The most recent incident to attract attention occurred on Aug. 20, 2011. At about 9 p.m., flight crews on airplanes passing over Shanghai reported seeing strange clusters of lights in the sky. The captain of one flight described the lights as “hundreds of times larger than the moon.” Witnesses on the ground in Beijing, Shanxi province, and the Inner Mongolia Autonomous Region also observed the same phenomenon.

Shortly after, Liu participated in UFO research seminars in Shanghai and Beijing. Based on his analysis of photos and eyewitness reports, he suggested that the unidentified lights might have come from around 200 kilometers west of the city of Bayannur in Inner Mongolia. He wrote in his report, “This UFO is very similar to the light phenomenon on the night of June 18, 1982, and can be classified in the same category — caused by a man-made spacecraft.”

Years of case studies have increased Liu’s confidence in his explanations. “I’ve done the math many times,” he says, adding that UFOs occurring at above 100 kilometers in the shape of a spiral, arc, horn, or spring tend to simply be caused by high-altitude man-made aircraft, such as residual traces formed by leftover fuel released by jettisoned rockets.

From this perspective, the decline in UFO reports can be explained by the increase in open data and information available to the public. Zhang remembers one night in the 1990s when he was waiting for a bus at the foot of Purple Mountain and spotted an object even brighter than Venus moving rapidly across the sky. At first he was taken aback, but he quickly realized it was a man-made satellite. This was not only because Zhang specializes in satellites but also because it had been reported that an out-of-control, Chinese-made satellite was expected to crash-land in the coming days. As the satellite was close to Earth, it could easily be detected with the naked eye.

Technological advances have also made it easier for the truth to emerge. Years ago, Liu’s colleague Wang Sichao called for the establishment of a rapid observation network for UFOs, allowing people to notify observers in different locations about major sightings through text messages, phone calls, and social media. At the time, Liu liked the idea, though it was difficult to realize. Now, the cost of 24-hour wide-field cameras covering the entire sky is much lower, and widespread smartphone ownership means that UFOs are easier to photograph. After analysis, most are found to be airplanes, balloons, kites, meteors, or rockets, and the mystery disappears in a flash.

Growing scientific literacy among the public also has brought more clarity. Zhang recalls that his parents started to grow a certain kind of mushroom in the 1980s because of a rumor that it was a cure-all, but today even middle school students are able to ask him and other scientists complex, cutting-edge questions about dark matter and gravitational waves.

So, should we still believe in aliens? A few years ago, Liu translated Stephen Webb’s book “If the Universe Is Teeming With Aliens ... Where Is Everybody?” The basic premise of the book is that we have yet to find even the slightest trace of intelligent extraterrestrial life, so in all likelihood humans are alone in the universe.

However, Liu has not shared this theory with his 10-year-old grandson, who has an interest in aliens. “The search for aliens is an expression of humanity’s curiosity — I don’t want to discourage him,” he says. “All living things need to explore and understand their surroundings to survive. This creates curiosity and a desire for knowledge. For humanity, this is what drives progress.”

Reported by Chen Shuyi.

A version of this article originally appeared in Shanghai Observer. It has been translated and edited for brevity and clarity, and published with permission.

Translator: David Ball; editors: Xue Yongle and Craig McIntosh.

(Header image: Visuals from VCG, reedited by Sixth Tone)