Answer;
D. The periphery of the photosphere appears darker than the center.
Explanation;
- Limb darkening is the phenomenon whereby the Sun is darker near its limb than near the center of its disk.
- Photosphere is the region in the solar atmosphere from which most of the visible light escapes into space and the limb is the apparent edge of the Sun as seen in the sky.
- Limb darkening is the feature in which the sun appears darker near the edges.