This is yesterday afternoon's sun photographed with a telescope and a sunscreen. It is a picture obtained by combining two photos: one to show the radiated light (the rays) and one to show as much as possible the surface of the sun. Since the higher layers of the photosphere are colder than the deeper ones, the image of the Sun appears brighter in the center, and becomes softer as it moves toward the edge of the visible disc's perimeter; this phenomenon is called obscuration at the edge, and is caused by a phenomenon of perspective. The surface is grainy because of the phenomenon of convection and, if it’s disturbed by the strong magnetic field, it will create black spots called sunspots. These have a lower temperature than the rest: "only" 4000 degrees, approx.
October 3, 2018