Figure 9-2Limb Darkening The Sun’s edge, or limb, appears distinctly darker and more orange than does its center, as seen from Earth (see Figure 9-1). This phenomenon occurs because we look through the same amount of solar atmosphere at all places. As a consequence, we see higher in the Sun’s photosphere near its limb than when we look at its central regions. The higher photosphere is cooler and, because it is a blackbody, darker and more orange than the lower, hotter region of the photosphere.