Original title: Starry sky has about | The brightness is the highest on the 26th! Look at this wonderful variable star
Xinhua News Agency, Nanjing, May 24 (Reporter Wang Juepon, Qiu Bingqing) On the 26th, a star that can't be seen with the naked eye most of the time, Cassiopeia R, will reach the maximum brightness of 4.7 stars and so on. The interested public can look to the northeast of the sky after midnight and try to observe the star with the naked eye.
The apparent magnitude of R Cassiopeia varies from 4.7 to 13.5 degrees, and the average cycle of brightness changes is about 430 days. Within each cycle, about two months can be seen with the naked eye. In the eyes of observers, it seems that every year or more, this star appears in the sky "out of nowhere" for about two months.
"In fact, this star does not grow out of thin air, but its brightness changes so that it is sometimes bright enough to be seen and sometimes invisible." Wang Kechao, director of science popularization at the Zijinshan Observatory of the Chinese Academy of Sciences, introduced that in astronomy, stars or star systems whose brightness changes frequently, such as Cassiopeia R, are called variable stars. There are many reasons for their brightness changes, such as pulsating variable stars and explosive variable stars, due to the changes in the physical state of the stars themselves; There are also brightness changes caused by the mutual eclipse of celestial bodies, such as eclipsing variable stars.
"Pulsating variable stars can also be divided into many types, such as Cepheid variable stars, Mira variable stars, etc." Wang Kechao said that Mira variable stars belonging to Cassiopeia R are red giant stars that have evolved to the later stage. Due to expansion and contraction, the star radius, temperature, and brightness change. This type of variable star is characterized by its reddish color, its light variation period usually exceeds 100 days, and its luminosity variation exceeds one apparent magnitude.
Cepheid variable is a pulsating variable with a very stable period. The most typical is Cepheus delta star, namely Cepheid I. Cepheid 1 is a binary star system composed of two stars. Due to the expansion and contraction of the host star, its apparent magnitude varies between 3.6 and 4.3. Its light cycle is 5 days, 8 hours and 47 minutes, which is as accurate as a clock.
Unlike pulsating variable stars with stable light variation period, the luminosity of explosive variable stars such as nova and supernova will change dramatically in a short time. For example, type Ia supernova is caused by the sudden collapse of a white dwarf star after it reaches the upper mass limit, resulting in a violent explosion.
The "star" in the eclipsing variable star is the second bright star in Perseus. Wang Kechao introduced that the Great Tomb Five is a system composed of three stars: the Great Tomb Five Aa1, the Great Tomb Five Aa2 and the Great Tomb Five Ab. Its brightness is usually maintained at about 2.1, and it will drop to about 3.4 in nearly half a day every 2.86 days. This brightness change is caused by the mutual concealment of Aa1 and Aa2.
