A world-class astronomical observatory is located in China’s “no man’s land”, Lenghu is no longer “cold”!

Lenghu Town, located in Mangya City, Haixi Mongolian and Tibetan Autonomous Prefecture, Qinghai Province, has a nickname - Mars Town because of its sparse population and extreme desolation.

In 2017, Deng Licai's team from the National Astronomical Observatory of the Chinese Academy of Sciences set foot on this isolated uninhabited area. The purpose of their trip was to find a world-class optical observatory site like the mountains in northern Chile, Mauna Kaya in Hawaii, and the Antarctic ice dome area. In 2021, when the team published a paper in the journal Nature, it quickly caused a sensation in the international astronomical community: Chinese scientists have found a potential astronomical observation site that can be compared with the world's top observatory sites, and it is the only world-class astronomical observation base in the Eastern Hemisphere so far!

At the beginning of 2024, Deng Licai's team won the title of "2023 Chinese Academy of Sciences Annual Team". Behind this honor is the story of building a world-class first-class astronomical observation base from scratch.

The dome of the AIMS telescope on Mount Saishiteng (Photo credit: National Astronomical Observatories, Chinese Academy of Sciences)

Strategic scarce resource optical observatory

Optics is the foundation of astronomy, and optical observatory sites are extremely valuable strategic and scarce resources in the field of astronomy. For example, Chile, relying on a large area of ​​excellent observatory sites, has vigorously promoted the development of astronomy as a national policy, attracting 68% of the world's ground-based optical/infrared and high-frequency radio astronomy observation facilities to settle there, winning huge development opportunities and space.

The site selection of an excellent optical observatory must take into account scientific factors such as seeing, water vapor, and the number of sunny days, as well as logistical factors such as transportation, communications, and water and electricity. It is very rare. In my country, the long-term lack of world-class observatory sites that meet the relevant conditions has always plagued the development of the discipline. Therefore, the site search for a world-class observatory is of great significance and is related to the performance of my country's future aerospace activities and related basic disciplines in international competition.

Seeing of 0.75 arc seconds is not easy to come by

As early as the second scientific expedition to the Qinghai-Tibet Plateau, the Lenghu area became an optional optical observation site. It has abundant sunshine, extremely low precipitation, clear night skies, and historical records show that the weather conditions were very good. After a series of preparatory work, Deng Licai's team locked in Saishteng Mountain in Lenghu as the site.

Since 2018, with the support of the local government, the team has gone through many difficulties and carried the necessary instruments and equipment to the mountain by hand and on their shoulders. They have selected a fixed site at an altitude of 4,200 meters in the Saishiteng Mountain area of ​​Lenghu (Saishiteng C area) to continuously monitor the number of clear nights, clear night background brightness and weather in the relevant areas, and obtained a large amount of useful key monitoring data. During this period, in order to ensure the continuity of parameter monitoring, team members ventured to climb dozens of times and upgraded and maintained the equipment in the severe cold. The three years of site selection, construction and monitoring can be said to be full of hardships.

Finally, through three consecutive years of data, the team came to a surprising conclusion - the median seeing value at the site was 0.75 arc seconds. What does this mean?

Seeing refers to the clarity of the image displayed by the telescope. Arc seconds are the unit of angle measurement, 1 arc second equals 1/3600 degree. A median seeing value of less than 1 arc second is considered ideal for astronomical observations. The median seeing value in Lenghu is only 0.75 arc seconds, which means that it is basically the same as the data of several internationally recognized top observatories during the same period, and the local atmospheric stability is extremely excellent. This has also become the biggest highlight of this site.

The only cabin on Mount Saishiteng where people could stay overnight when the site was initially selected (Photo source: National Astronomical Observatory, Chinese Academy of Sciences)

Regulations protect "Dark Sky Reserves"

In addition to the basic conditions for a world-class observatory, such as many high-quality clear nights, cold and windy weather, dryness and little rain, Deng Licai said that the light environment in Lenghu can be said to be one of the darkest in the world.

As a strategic scarce resource, Lenghu Observatory must do its utmost to avoid light pollution. To this end, the 35th meeting of the Standing Committee of the 13th People's Congress of Qinghai Province reviewed and approved my country's first local regulation on dark sky protection - "Regulations on the Protection of Lenghu Astronomical Observation Environment in Haixi Mongolian and Tibetan Autonomous Prefecture", which divides the Lenghu astronomical observation environment into a dark night protection core area and a dark night protection buffer area. Very strict lighting control conditions are formulated in the core area within a 50-kilometer radius of the observatory site, and a 50-kilometer radius outside the core area is a buffer area to restrict the development of lighting. Because it is located in an uninhabited area, the relevant regulations will not affect the lives of residents.

Starting from January 1, 2023, the "Regulations on Environmental Protection of Lenghu Astronomical Observation in Haixi Mongolian and Tibetan Autonomous Prefecture" will be officially implemented, and the dark night sky will have its own legal guardian.

Oil town transformed into astronomy town

In the 1950s, rich oil resources were discovered in the Lenghu area, and oil workers built their homes in the desert. Lenghu was once known as the "Oil Town", but as resources gradually dried up, the area fell silent again after the 1980s. With the construction of the Lenghu Astronomical Observatory, 12 research projects from 11 scientific research institutions and 43 telescopes have been built in Lenghu in recent years, and the area has become the largest astronomical observation base in Asia.

Nowadays, every summer, children from all over the world come to Lenghu to observe the fascinating space through telescopes and fall in love with science through close contact with science and scientists. Lenghu has also transformed from a declining oil town to a bustling astronomy town.