Tibet will build the world's largest refracting telescope? Why did you choose to build in Tibet? Why not build reflecting telescope?

China will build the world's largest refracting telescope, led by the National Astronomical Observatory of Chinese Academy of Sciences, and jointly built by Purple Mountain Observatory of China Academy of Sciences and Tibet Museum of Natural Science. The construction site is Lhasa, which is located on the Qinghai-Tibet Plateau on the roof of the world. After completion, it will be applied to scientific research and popular science day and night. The telescope will be located in the newly-built Tibet Planetarium, not only for astronomical research, but also open to the public for tourists to visit and use.

This plan is exciting enough, because there are four characters "the largest in the world" in it! Of course, it would be superficial to stop here. ...

This is the largest optical telescope? It's not like that ... students who don't know much about astronomy may be excited in vain, because the diameter of the optical telescope planned to be built this time is "only" 1 meter, which is really dwarfed by the telescopes of major ground optical observatories in the world, because as early as 100 years ago, the reflective optical telescope-Hooke telescope with a diameter of 2.54 meters was built at Mount Wilson Observatory in California, USA, which is astronomy.

At present, the largest single-aperture optical telescope in the world is the Keck Telescope located on Monaque Mountain, which consists of two reflective telescopes with a diameter of10m. Astronomer Andrea Gates, who won the Nobel Prize in physics last year for her observation of the black hole in the center of the Milky Way, made observations through it. It can be seen that a high-performance large-aperture telescope has great achievements in scientific research.

By contrast, our 1m optical telescope is really a little brother ... but you must find that people in China are not bad. These large-aperture optical telescopes abroad are reflective, while what we want to build is refractive. Although in the optical telescope, the aperture of 1 m is really just a little brother, but in the refractive telescope, it is really the first in the world!

What's the difference between a refracting telescope and reflecting telescope? In fact, both large-aperture telescopes on the ground and space telescopes in the sky are basically reflective, because the manufacturing difficulty and weight of refractive telescopes will increase sharply when they reach a certain caliber.

Refraction telescope should be the oldest telescope. It is optically amplified by a set of glass lenses. Galileo looked into space with a homemade refracting telescope, which opened the era of modern observational astronomy.

However, with the increase of aperture, the difficulty of lens manufacturing will increase sharply. In addition, the lens itself will cause the dispersion phenomenon of synthesized light with different frequencies, resulting in chromatic aberration, that is, you will see several images with different colors at the same time. Although the color difference can be reduced to some extent, it will also affect the color reproduction. Therefore, after reaching a certain aperture, people often choose reflective design. The reflective primary mirror is changed from a convex lens to a concave mirror, and the light is reflected by the coating on the mirror surface, but it does not pass through the glass lens in the process of light convergence and will not produce color difference. However, the reflective telescope has an obvious disadvantage that the mirror exposed to the air for a long time will accumulate dust and reduce the reflective performance, so it needs to be re-coated regularly, which is relatively troublesome to maintain.

Why choose a refracting telescope? Then the problem is coming. Refractive telescopes seem to have many shortcomings. Why did you choose to build a refracting telescope? This is determined by its use. Telescopes are dual-purpose and open to the outside world. In addition to astronomical observation at night, it can also be observed on the ground during the day. However, reflective telescopes are not suitable for ground observation. Due to its structure, the mirror has a small field of view and low picture contrast under large aperture, which is prone to coma. Refractive telescope has a large field of view and bright colors, which is more suitable for landscape measurement with a positive mirror. (DuDu in a low voice: In other words, are you sure that our titanium alloy eyes will not be blinded by daytime observation with a caliber of 1 meter ...)

A holy place for astronomical observation

Ask where to see the stars on the internet. Apart from the conventional answer that there is no light pollution in the suburbs, the answer with a definite place name must be the highest "appearance rate" in Tibet! Why does everyone push Tibet first? In fact, the answer is very simple. At high altitudes, the air is thin and there is less light pollution. High altitude and thin air are the most unique places in Tibet. We all know that the Hubble Space Telescope has a main mirror with a diameter of more than two meters, which is smaller than many ground telescopes, but it is the clearest telescope for human beings at present! The reason is that it is located in an almost vacuum space environment far from the ground.

Higher altitude, thinner and drier air make the starlight from far away less scattered and disturbed. The positions of large optical telescopes on the ground are basically at high altitude. For example, the Keck telescope, the largest optical telescope in the world mentioned above, is located at the top of Mauna Kea Mountain in Hawaii, with an altitude of 4 145 meters.