According to China's ancient book Song Dynasty, there was a very bright piece in A.D. 1504. In fact, this guest star is what we think.

The answer is obviously D, the remnant of supernova 1054, which is now the famous Crab Nebula.

Red giant star is a stage when the star begins helium fusion after 10 thousand years, its volume expands greatly, its surface temperature drops, and its luminous ability will increase greatly. It can last for quite a long time, such as the solar duration 1 100 million years or so. And there are so many red giants in the whole sky, including Antares and Betelgeuse in the first-class stars. Has the brightness changed abnormally for thousands of years?