Tibet will build the world’s largest refracting telescope? Why choose to build in Tibet? Why not build a reflecting telescope?

Our country will build the world's largest refractor telescope. It will be led by the National Astronomical Observatory of the Chinese Academy of Sciences and jointly undertaken by the Purple Mountain Observatory of the Chinese Academy of Sciences and the Tibet Natural Science Museum. The construction site is located on the Qinghai-Tibet Plateau, the roof of the world. Lhasa. After completion, it will be able to be used for scientific research and popularization all day and night. The telescope will be set up in the newly built Tibet Planetarium. In addition to conducting astronomical research, it will also be open to the public and tourists can visit and use it.

This plan is enough to make people excited, because it contains the four characters "the world's largest"! Of course, you would be too superficial if you stopped there... Is this the largest optical telescope? Not...

Students who don’t know much about astronomy may be excited because the diameter of the optical telescope planned to be built this time is “only” 1 meter, which is different from the telescopes of the world’s major ground optical observatories. It pales in comparison, because as early as a hundred years ago, the Mount Wilson Observatory in California, USA, built a 2.54-meter-diameter reflecting optical telescope - the Hooker Telescope, which was the astronomical telescope through which astronomer Hubble first discovered the expansion of the universe. !

The world's largest single-aperture optical telescope is the Keck Telescope located on Mauna Kea, Hawaii. It consists of two reflecting telescopes with an aperture of up to 10 meters. Astronomer Andrea Gates, who won the Nobel Prize in Physics last year for her observations of the black hole at the center of the Milky Way, made observations through it. It can be seen that the high-performance large-aperture telescope is an artifact that has achieved significant scientific research results.

In comparison, our 1-meter optical telescope is really a little brother... But if you are good at Chinese, you must have discovered that these large-diameter optical telescopes abroad are all reflective, and What we are going to build is refractory. Although in optical telescopes, the 1-meter diameter is indeed just a little brother, in refractor telescopes, it is indeed the first in the world! What is the difference between a refracting telescope and a reflecting telescope?

In fact, whether it is a large-diameter telescope on the ground or a space telescope in the sky, they are basically reflective. This is because when a certain diameter is reached, the manufacturing difficulty and weight of refracting telescopes will be staggering. increase.

The refracting telescope should be the oldest telescope. It achieves optical magnification through a set of glass lenses. Galileo used a homemade refracting telescope to look into space, ushering in the era of modern observational astronomy.

But as the diameter increases, the difficulty of manufacturing the lens will increase sharply. In addition, the lens itself will cause dispersion of synthetic light of different frequencies, resulting in chromatic aberration. That is, you will see several different colors at the same time. Like, although chromatic aberration can be reduced to a certain extent, it will also affect the restoration of color. Therefore, after reaching a certain caliber, people often choose a reflective design. The reflective main mirror is changed from a convex lens to a concave mirror, which reflects and gathers light through the coating on the mirror surface. The light does not pass through the glass lens during the condensation process, and no light is produced. Color difference. However, an obvious disadvantage of reflecting telescopes is that the mirror surface that is exposed to the air for a long time will accumulate dust and reduce the reflection performance. Therefore, it needs to be re-coated regularly, and maintenance is relatively troublesome. Why choose a refractor telescope?

Then the question is, it seems that the refractor telescope has many shortcomings. Why choose to build a refractor telescope? This is determined by its purpose. The telescope is used both in the sky and on the ground and is open to the public. In addition to conducting astronomical observations at night, it also conducts ground observations during the day. The reflecting telescope is not suitable for ground observation because of its structure. The field of view is small, the picture contrast is low, and coma aberration is prone to occur. Refracting telescopes, on the other hand, have a relatively large field of view and bright colors, and are more suitable for landscape surveying when equipped with an erecting mirror. (Beep quietly: By the way, are you sure that daytime observation with a 1-meter diameter will not blind our titanium alloy eyes...)

A holy place for astronomical observation

Inquire online where to go Looking at the stars, in addition to the common answers here where there is no light pollution in the suburbs, among the answers with definite place names, Tibet must be the one with the highest "photography rate"! Why does everyone recommend Tibet? In fact, the answer is very simple. The altitude is high, the air is thin, and there is less light pollution. The high altitude and thin air are the most unique features of Tibet. We all know that the Hubble Space Telescope has a primary mirror with a diameter of more than two meters, which is smaller than many ground telescopes, but it is currently the clearest telescope in mankind! The reason is that it is located in an almost vacuum space environment far away from the ground.

Higher altitude and thinner and drier air cause less scattering and disturbance of starlight coming from a distance. Large optical telescopes on the ground are basically located at high altitudes. For example, the Keck Telescope, the world's largest optical telescope mentioned earlier, is located on the top of Mauna Kea in Hawaii at an altitude of 4,145 meters.