Why does the Sun’s disk have a sharp edge?

The sun is a gaseous, more precisely, a plasma ball, and therefore it cannot have a sharp boundary, like a liquid or solid. However, at the Sun, the transition to complete opacity of matter occurs in a layer only 300 km thick, which, from a distance of 150 million kilometers, gives a sharp boundary.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.