Sky classroom | Those things to measure the brightness of the stars

Hello friends, everyone,

The "Air Class" of the Astronomical Museum is class!

The astronomical term that measures the brightness of celestial bodies is called "metering". The history of people's measuring star brightness can be said to be the history of the improvement of light metering instruments. At the same time, due to the particularity of the measurement target, the method is mainly used to mark the brightness of the target.

Celestial brightness measurement has gone through several stages. The first stage is the visual stage. It is estimated that the brightness of the celestial body is the first stage with the eyes of the eyes or the help of the eyes (naked eyes). The invention of the telescope only increases the ability to see the dark star, which has nothing to do with the improvement of the accuracy of the metering. Although the observation results of each observer are obtained from the brightness of the previous star table, due to the large difference in individuals, the brightness level of the birth standard during the metering period does not have a birth standard. In the 100th BC, the ancient Greek astronomer, Starchas, was widely accepted by the visual stars. This agreement is still being used to this day.

But for darker stars, there are large errors between different star watches at the visual stage. Even now, some enthusiasts have visually optical testing of some bright stars. These meter results are used by astronomers to study the changes in celestial body brightness (see Figure 1).

Figure 1 visual ginseng four -light curve

Photo source: https://www.aavso.org/about-light-curves

The second phase of the metering is to measure the brightness of the celestial body by using the optical meter, rather than the use of the naked eye directly. These optical meters are usually used with the telescope to achieve the purpose of measuring dark stars. The brightness of a star by the glass diagonal or the Nichor prism is attenuated to make it consistent with the brightness of another star, which can accurately compare the difference between the two stars brightness. In the field of light metering, the biggest achievement at this stage is to fix the brightness level of the stars, and use mathematical language descriptions, that is, 5 such differences such as stars, and the brightness difference is 100 times.

The third stage of metering is due to the invention of photography. With the advancement of chemical photosensitive materials, with the increasingly large -caliber astronomical telescope, photography light metering technology has improved rapidly. It is worth mentioning that because the photography negative is more sensitive to the short -wave purple light, it is very different from the human eye, which leads to the birth of two measurement stars and other systems, that is, according to Xiangxing and other viewing stars. This further led to the discovery and application of the concepts of star color and total radiation.

After 40 years of photography, the photoelectric effect was discovered, and after 100 years, the optoelectronic double -tube was invented. The optoelectronic pipes expand the range of detection of celestial body wavelength, while greatly improved the measurement accuracy. Soon after that, the electrolytic device (CCD) was born. CCD completely changed the astronomy of the optical band. With the popularization of CCD and the decline in costs, amateur enthusiasts can shoot images that have only been exposed for long -term exposure of large -scale astronomical telescopes with small devices. In recent years, the complementary metal oxide semicides (CMOS) has become closer and closer to CCD in terms of performance. CMOS sensors have more advantages in high -frequency record data. I believe that new discoveries of astronomy in the further development of CMOS sensors.

(Beijing Astronomical Museum)

Public account name: Beijing Institute of Science and Technology, Beijing Science and Technology Research Institute

WeChat: BJAST-WX

Welcome everyone to follow us!

- END -