The gas vortex on the surface of the sun is slightly lower than the temperature in the adjacent area, and looks like a black spot on the surface of the sun from the earth, so it is called a sunspot. The discovery of sunspots originated in China. Huainanzi, written about 140 BC, has a description of "horses in Japan and China", which should be the earliest sunspot record. The record of sunspots in Hanshu Wuxing Zhi is more detailed: "The first year of peace ... March has passed, the sunrise is yellow, and the black gas is as big as the money line, living in the center of the sky." This is a record of sunspot phenomenon seen in March of the first year of Heping in the Western Han Dynasty (28 BC). The earliest record of sunspots in Europe was on August 19, 807, but it was mistaken for the transit of stars. The discovery of sunspots is one of the astronomical advances made by Galileo with his telescope. He only saw sunspots at 16 10, and published the results at 16 13.