Solar Disc

I thought it sounded a bit different to 'Sun'. Several facts about the Sun as seen in this image; the brighter centre is due to us seeing towards the burning heart of the Sun, the limb darkening towards the edges is due to us seeing more obliquely through layers of cooler atmosphere. AR2271, the group to the upper right of the image display the 'Wilson Effect'. This is where because of the perspective we see  the central dark umbra of the sunspot appearing depressed into the Sun's 'surface'. Finally, as well as the dark sunspots (appearing dark because they are cooler than the general surrounding surface) there are brighter streaks seen at the Sun's limb called faculae; these are hotter than the underlying surface and are easier to see in contrast at the edges of the solar disc.