Where is the most brilliant starry sky? China's large optical observatory is located on the Qinghai-Tibet Plateau

Looking up at the stars is the oldest human behavior, but the use of telescopes to explore the stars has only a history of more than 400 years. During these 400 years, human beings have made rapid progress in their understanding of the universe, and at the same time, they have overcome many technical difficulties, one of which is how to find a clear sky for the telescope to allow humans to explore the universe unimpeded.

High-quality astronomical observations cannot be carried out everywhere. It has very strict requirements on the atmosphere, and the air must be extremely transparent and quiet. We all have the experience that the stars in the sky often "blink", which is caused by atmospheric tremors, which is not conducive to astronomical observations. In addition, there are many stringent requirements, such as less pollution, more sunny days, and very little water vapor and dust in the air. Therefore, it is not easy to obtain a high-quality astronomical observation point. It is a goal that astronomers dream of but is not easily achieved. Especially in today's highly developed industrialized human society, it has become particularly difficult to achieve this goal.

In August 2021, Chinese scientists announced a major scientific breakthrough. Astronomers overcame numerous difficulties and, after unremitting efforts, successfully discovered an excellent observatory site in Qinghai Province - the Qinghai Lenghu site. Lenghu is a lake on the Qinghai-Tibet Plateau, located in the Gobi Desert at the southern foot of the Altun Mountains in northern Qinghai Province, my country. The town of Lenghu, named after the lake, is also located nearby. Scientists found this very ideal astronomical observation point near Lenghu Town, which is located on a peak at an altitude of 4,200 meters in the Saishiteng Mountain area of ​​Lenghu. Finding an excellent observatory site requires a tenacious spirit that is not afraid of difficulties and a rigorous scientific attitude.

Since January 2018, the research team of the National Astronomical Observatory of the Chinese Academy of Sciences has continuously monitored various parameters in the Lenghu area for three years. The results show that the Lenghu area has abundant sunshine, scarce precipitation, and clear night skies. Due to the high terrain, ground wind and sand have no impact on areas above 4,000 meters. At the same time, the weather conditions recorded in historical records are also very ideal. Therefore, scientists believe that the observation conditions here have world-class seeing and the potential to host major astronomical scientific facilities in my country in the future. It can be called a "world-class astronomical observatory site" and can be compared with the world-recognized best observatory site such as Mauna Kea in Hawaii.

The Qinghai-Tibet Plateau is known as the "third pole" of the world and is a place that the international astronomical community longs for. Now, Chinese scientists have finally found the best astronomical observatory site here, thus realizing the common wish of astronomers around the world. This achievement has broken the bottleneck that has long restricted the development of optical astronomical observation in my country, and created major opportunities for the development of optical astronomy, planetary science, deep space exploration and other disciplines in my country.

Excellent site makes ground-based astronomy brilliant

Today, astronomy has entered the era of multi-messenger multi-band time domain. People observe the universe not only with visible light, but also with many other invisible lights, including radio waves, infrared, ultraviolet, X-rays, gamma rays, etc. For this reason, telescopes are no longer limited to traditional ground-based telescopes. Space telescopes are also constantly looking into deep space to explore the universe.

However, even today, ground-based telescopes are still the main force in astronomical research. This is because space telescopes are expensive to build, difficult to launch and operate, and still limited in caliber and observation capabilities. Therefore, in the bands that can penetrate the atmosphere, people still rely mainly on ground-based astronomical telescopes to observe the universe. Specifically, visible light, radio waves, and some infrared rays can penetrate the earth's atmosphere and reach the ground, and ground-based telescopes have made great achievements in these bands. In fact, it is precisely because of large ground-based telescopes that human beings have made great progress in understanding the universe.

In 1917, people built the 2.5-meter-diameter Hooker Telescope at the Mount Wilson Observatory, which was the largest astronomical telescope at the time. Mount Wilson is located near Pasadena, California, USA, with an altitude of 1,742 meters. It has a wide field of view and a stable atmosphere, which is very suitable for astronomical observation. Shortly after the Hooker Telescope was built, American astronomer Edwin Hubble came to Mount Wilson and began to use the Hooker Telescope to study the universe. At that time, many people believed that the "Andromeda Nebula" was just a "nebula" that existed in the Milky Way, and the Milky Way was also very special and unique in the universe. However, Edwin Hubble used the Hooker Telescope to see the stars in the "Andromeda Nebula", which showed that the Andromeda Nebula was not a "cloud", but was composed of stars, and was a "galaxy" like the Milky Way.

Mount Wilson Observatory

Moreover, Edwin Hubble also judged that this galaxy existed far away from the Milky Way through the "Cepheid variable stars" in the Andromeda Nebula, which is an important guarantee for the future development of Chinese astronomy. It turns out that the Milky Way is not special, it is just an ordinary galaxy in the universe. Edwin Hubble showed a strong interest in galaxies. After studying many galaxies with the Hooker telescope, he found that almost all galaxies showed red shift. This shows that all galaxies in the universe are moving away from us, and the speed at which galaxies are moving away is closely related to their distance from us: the farther they are, the faster they move away from us. So Edwin Hubble understood that the recession speed of galaxies is proportional to their distance.

It turns out that the universe is expanding, it is not static, and it is performing movement, change, birth and death at every moment. This discovery changed the human view of the entire universe. The outstanding performance of the Hooker telescope inspired astronomers. Since then, the development of ground-based telescopes has entered the fast lane, and various large ground-based telescopes have emerged in an endless stream. They are located in places with ideal observation conditions, such as the Mauna Kea Observatory located at an altitude of 4,206 meters on the Mauna Kea volcano, where the Keck telescope, the Subaru telescope and the Gemini North telescope are all installed.

The European Southern Observatory in Chile was founded in 1962 and is home to an amazing telescope, the Very Large Telescope. It is located on the Paranal Mountain at an altitude of 2,632 meters, where the climate is dry and the night sky is clear, making it ideal for astronomical observations. After years of planning and construction, the large binocular telescope was finally built on Mount Graham at an altitude of 3,190 meters in Arizona, USA. Far from the lights of big cities, there is very little water vapor and dust, making it an ideal astronomical observation point. Since the 1990s, more than a dozen large telescopes with an aperture of 8 to 10 meters have been erected in the Western Hemisphere, a grand move that has greatly promoted the development of astronomy.

Mauna Kea Observatory on Mauna Kea

An important guarantee for the future development of Chinese astronomy

In this context, the construction of ground-based telescopes in my country is also developing. In the family of optical telescopes, my country already has a 2.16-meter-diameter telescope located at the Xinglong Observatory of the National Astronomical Observatory; a 2.4-meter-diameter telescope located at the Lijiang Observatory of the Yunnan Astronomical Observatory; and the larger-diameter LAMOST is a 4-6-meter-class spectral survey telescope, also located at the Xinglong Observatory. LAMOST was later officially named the "Guo Shoujing Telescope". It is the world's largest large-field telescope and can be called a capable "starry sky inspector." It has the function of "surveying" the starry sky, but does not have imaging observation capabilities.

Guo Shoujing Telescope

Whether it is the Purple Mountain Observatory, Yunnan Observatory, or the Xinglong Observatory of the National Astronomical Observatory, these early observatories all met the observation needs of the time. However, as time goes by, astronomers need to locate the next generation of astronomical telescopes in a more ideal place, which requires astronomers to truly find sites according to international standards.

This work started around 2000, and since then, Chinese astronomers have turned their attention to the western part of my country. In 2016, the "13th Five-Year Plan for the Construction of Major National Science and Technology Infrastructure" was officially announced, and the large optical infrared telescope was listed among the 10 priority projects, thus clarifying the goal of "selecting the best site and building a 12-meter-class optical infrared telescope." This is a grand plan to sprint to the limit of optical detection capabilities. If there is a 12-meter-class optical infrared telescope, my country's comprehensive astronomical observation capabilities can be greatly improved, which will help it to rank among the world's leading ranks.

At the same time, this project can also provide important support for cutting-edge research in related fields and drive the innovative development of advanced optical technology in my country. For this reason, Chinese scientists began to select the site for the observatory based on the standards of a 12-meter-class optical infrared telescope. Lenghu is located in the hinterland of my country. As the site of a future large-scale observatory, the Lenghu Observatory Base has the conditions to develop good transportation facilities, build reliable logistics support and scientific research bases. Now, with the recognition of experts, some projects have begun to settle in the Lenghu Observatory Base. In May 2021, the 2.5-meter wide-field survey telescope project of the University of Science and Technology of China-Purple Mountain Observatory, with a total investment of 200 million yuan, settled in Lenghu. After completion, this telescope will become the largest and most capable telescope for time-domain survey observations in the northern hemisphere.

At the same time, the Qinghai Provincial Government and Tsinghua University signed a cooperation agreement for the "Wide Field Survey Telescope (MUST)" project with a total investment of about 1.3 billion yuan. The 50-centimeter binocular telescope jointly built by China West Normal University and the National Astronomical Observatory has been stationed and has begun work. Judging from the projects that have been built and are under construction, Lenghu will become the largest observatory in my country, and it will also become an important resource for astronomical observations in the world. More importantly, it provides an important guarantee for the great strides of Chinese astronomy in the future.

At present, most of the world's large ground-based telescopes are concentrated in the Western Hemisphere. This uneven distribution has restricted the development of astronomy. This is because astronomical observations often require relay observations in the time and space domains, and the lack of excellent large observatories in the Eastern Hemisphere makes it difficult to complete such observations. Now, the emergence of the Lenghu Observatory will change this dilemma. The establishment of a large optical observatory in my country will not only bring major opportunities for the development of astronomy in my country, but will also make important contributions to the great cause of exploring the mysteries of the universe for all mankind.

Saishiteng in the sunset after the snow, with the observatory shrouded in the afterglow of the sunset. (Image source: National Astronomical Observatory of China)