Cold lake weather in Qinghai

Qinghai Lake is famous for its peculiar Ya Dan landform. Because it is barren and dry, and the landform is similar to that of Mars, it has a vast and far-reaching desolate beauty. High altitude, few people, abundant sunshine and clear night sky create excellent conditions for astronomical observation.

202 1 the Milky Way Arch on Tanabata was shot at the C point of Saishiteng under construction. Photo courtesy of Jerome Ang.

Panorama After the snow in Saishiteng in the winter of 2020, the whole observatory was shrouded in the afterglow of the sunset, and the vast Qaidam Basin was in the distance. Deng Gongtu

Find the best website

Optical/infrared observation stations are extremely precious and scarce resources. At present, the internationally recognized best locations are only the mountains in northern Chile, Mauna Kaya Peak in Hawaii, USA and the Antarctic inland ice dome. Among them, Chile, which has a large area of excellent observation sites, has made it a national policy to vigorously promote the development of astronomy, attracting 68% of the world's ground-based optical/infrared and high-frequency radio astronomical observation facilities, and the famous Very Large Telescope (VLT) built by the European Southern Observatory is located in Chile. The "settlement" of these astronomical observation facilities has won great development opportunities and space for Chile in cutting-edge research, cutting-edge technology and social economy.

Astronomical circles in China attach great importance to the site selection of optical astronomy, and began to deploy it in the western region of China in the 1990s. What are the requirements for the best site? Deng, chief researcher of the National Astronomical Observatory, said that observation from the ground to the air needs to penetrate the earth's atmosphere, so there are fewer cloudy days and more sunny days, and the quality of sunny days is better, that is, visibility is better.

He further explained that starlight reaches people's eyes and equipment through the atmosphere. The compression or expansion of the atmosphere leads to chaotic air flow, and the light will bend and shake when passing through these places, so people often see the stars "blink". "The more you blink, the worse your visibility."

If there is dust in the air, it will be absorbed or scattered by the atmosphere, so the local air must be particularly clean. In addition, in order to pursue the ultimate scientific goal, researchers need to observe infrared light with longer wavelength as an important means to obtain important astrophysical information. Because water vapor absorbs infrared light strongly, the water vapor content from the ground to the top of the atmosphere at the Observatory is particularly low.

These harsh conditions exclude many websites. Starting from 20 17, Deng's research team took advantage of the opportunity to carry out scientific research projects in Qinghai and cooperated with the local government of Lenghu, Haixi Prefecture, to start on-site search in the no-man's land in the west of Haixi Prefecture.

A cold lake without light pollution

Cold Lake, located in Haixi Prefecture, Qinghai Province, was once an important oil producing area in China. With the exhaustion of oil resources in 1980s, Lenghu gradually shrank into a small town with only 800 residents. It is precisely because of the small population that there is almost no light pollution in the local area, and the starry sky at night is particularly transparent.

Cold Lake is building a "Mars town" integrating science popularization, science popularization and science fiction with its geological and geomorphological environment resembling Mars and high-quality night sky resources. On 20 17, local cadres seeking transformation and development took the initiative to find Deng, hoping to introduce astronomical projects.

However, Deng also has concerns. He is worried that once this sparsely populated cold lake with beautiful starry sky develops into a punching point among network celebrities, it will destroy the original night starry sky resources. After a week of stagnation in cooperation and consultation, local cadres came to him with red-headed documents-the whole area of Lenghu was designated as a night reserve. "Light pollution is a problem faced by observatories all over the world. Cold Lake solved this problem before the project started. "

In May of 20 18, Deng's team visited Saishiteng Mountain in Lenghu Lake, leaving the first human footprint on this "Mount Notre Dame". "Saishiteng is Mongolian, which has two meanings. One is abrupt, just like a mountain suddenly rises on the Gobi, and the other means awakening. " Deng said that when the helicopter first sent him to Saishiteng Mountain at an altitude of 4,200 meters, he found that the local conditions were very ideal.

The cold lake area has long sunshine time, extremely low precipitation, clear night sky and very good weather conditions recorded in history. But in the past, people thought that there was dust here and it was not suitable for establishing an observatory. The situation at the scene subverted everyone's understanding. Deng said that if the mountain is gentle, the dust will move with it. However, there is a high mountain every short distance in the cold lake area. The height difference between Saishiteng and the Qaidam Basin below it exceeds 1000 meters, and dust rarely reaches the top. "Even if there is a sandstorm in Lenghu Town, once you reach the top of the mountain, the sky you see is still blue."

Climb a mountain with equipment on your back

Finally, the research group decided to make a fixed-point site selection at the elevation point of 4200 meters above sea level in the mountainous area (Saishiteng C area). Haixi state government calls helicopters to transport the building materials on the observation deck to the site. However, it is not easy to rely on Deng's team for the subsequent operation and maintenance of the parameter measuring equipment. At that time, there was no road leading to the monitoring point in the mountainous area, and the site selection team needed manpower to carry all kinds of instruments and equipment to climb the mountain.

"Up the hill to maintain and update the equipment about ten times. We climbed to the top of the mountain at an altitude of 4200 meters from the mountainside of 3200 meters that can be reached by off-road vehicles at the foot of the mountain. " Facing the challenge of altitude sickness, Deng, who loves mountaineering, needs two and a half hours to climb six kilometers with 10 kg of materials on his back, while his colleagues need three to five hours. This arduous task is always accompanied by danger. On one occasion, Deng slipped and fell down the slope, which ended in a cliff. He quickly stretched out his limbs to increase the friction area, which stopped. He said that all the members of the project team had similar experiences, and some even spent the night in the barren hills.

In the early winter of 20 18, Deng was on his way to climb the mountain. Photo courtesy of Tian Cairang

The conditions on the mountain are even worse. "Wear polar down jackets and down trousers when sleeping at night, get into a sleeping bag at MINUS 30 degrees Celsius and cover five quilts, which is barely cold enough." Because of this, researchers have made great efforts to develop software that enables researchers to observe and control equipment remotely.

The team overcame many difficulties and finally obtained the conclusive data of the optical/infrared observation conditions of Saishi Tengshan. In order to avoid the interference of various non-scientific factors on the site selection of large astronomical observation facilities and ensure the reliability and fairness of data, all the original data collected by the project are made public in real time during the whole site selection process.

Stars that don't blink.

By the end of 2020, the team has accumulated three years of site monitoring data. Statistical analysis shows that the median visibility of area C (4200m elevation point) in Saishitengshan of Lenghu Lake is 0.75 seconds. This parameter is roughly the same as the data of the international best site in the same period. In contrast, the Guo Shoujing Telescope (LAMOST) is located in Lian Yingzhai, Xinglong County, Hebei Province, with a viewing angle of 65,438 0.5 arc seconds, twice that of the former.

What is the concept of 0.75 arc seconds? Deng said that a circle was cut into 360 parts, each part was one degree, and once it was cut into 3600 parts, one of which was an angular second. 0.75 arc seconds is the smallest angle that the eyes can't distinguish. "The smaller the diopter, the more stable the observed celestial body. The stars you see in the city' blink' feel beautiful. From here, the stars are basically not flashing, which is very beneficial to astronomical observation. "

For extreme scientific goals such as the origin of matter and the origin of life, the best window is in the infrared band. Moisture in the atmosphere will strongly absorb infrared light, so the most important site index is condensable water vapor (PWV). In this index, the site of Saishiteng in Lenghu is the most superior among all the world-class sites in mid-latitude areas.

According to the comprehensive quantitative analysis of observable time and visibility, the quality of Saishiteng Mountain is better than other stations on the Qinghai-Tibet Plateau, and basically the same as that of Mauna Kaya Peak in Hawaii and other stations in Chile.

65438+On February 20th, 2020, the 50BiN telescope installed by China West Normal University and National Astronomical Observatory was tested and observed. This is the first light of the cold lake astronomical observation base, that is, an observatory or astronomical observation equipment looks at the target in the sky for the first time.

"The discovery of the world-class site of Lenghu has broken the bottleneck that has restricted the development of optical astronomy in China for a long time and created great opportunities for the development of optical astronomy in China." Deng said that especially the geographical longitude area where Lenghu is located is a blank area of large optical telescopes in the world, and astronomical observation often needs relay observation in time and space. Therefore, Cold Lake, a world-class site, is also a valuable resource for developing international optical astronomy.

Telescope anjia

In order to give full play to the scientific potential of Lenghu site, the Chinese Academy of Sciences will unite with the Qinghai provincial government to protect the site resources as soon as possible and avoid the influence of human activities such as lighting, on the other hand, make unified planning and layout for the development of major observation facilities in the future.

Deng said that in order to protect the dark night environment, the lighting, municipal lighting and household lighting of Lenghu enterprises have corresponding specifications, and violations will be punished. "The local resident population is very small. Travelers come to the desert to enjoy the starry sky and landforms, so neither tourists nor locals will destroy the dark night environment, and there is little pressure on the protection of the site. However, the government still attaches great importance to this and laws and regulations on night protection are taking shape. "

At present, the 2.5m sky survey telescope of China University of Science and Technology, the 1 Missong telescope and 1 m solar mid-infrared telescope of National Astronomical Observatory of Chinese Academy of Sciences, the 50 bin binoculars of China West Normal University and the1.8m and 80cm planetary observation telescopes of Institute of Geology and Geophysics of China Academy of Sciences have all been built on this platform. In the future, more telescopes will "settle down" here.

In May, 20021,Qinghai Province and Tsinghua University signed an agreement to build a 6.5-meter-wide field-of-view (spectrum) survey telescope in Qinghai Cold Lake in about seven years, and to carry out all-round astronomical research on this basis. Deng revealed that most telescope projects signed with Lenghu have entered the stage of construction and equipment installation, and the number of telescopes has reached 30 (one of which is in an array project). By then, Lenghu will become the largest observatory in China and even Asia.

"The next landing target in my mind is China's large-aperture optical/infrared telescope, 12 meter or more!"

Learn more: optical telescopes and radio telescopes

Optical telescope is the earliest telescope invented by human beings, which works in visible light (that is, light that can be seen by human eyes). Compared with human eyes, optical telescopes can increase the light concentration and improve the resolution, and are easy to aim at celestial bodies and observe for a long time. Guo Shoujing telescope is an optical telescope.

Limited by the size of the optical telescope, many distant celestial bodies cannot be detected by the optical telescope. Cosmic celestial bodies not only radiate visible light waves, but also constantly radiate electromagnetic waves with wavelengths greater than light waves. According to this phenomenon, scientists invented the radio telescope. A typical radio telescope is like a big pot cover, such as the FAST telescope. Because radio waves can pass through clouds and dust, they can be continuously observed by radio telescopes, which is not limited by rain and night.

Editor Fan Yijing proofreads Li Lijun.