For certain solar spectral lines, a lessening of the intensity of the line from the center of the solar disk to the limb, caused by the existence of a temperature gradient in the Sun and the line-of-s
ight through the solar atmosphere. Limb darkening also occurs in some radio wavelengths.
An apparent decrease in brightness of the Sun near its edge as compared to its brightness toward the center. Limb darkening is readily apparent in photographs of the Sun. The reason is that when we lo
ok toward the disk's center we look into deeper and hence hotter layers along the line of sight. Toward the limb, we get radiation from higher and hence cooler and less bright layers of the photosphere. Limb darkening has been detected in the case of several other stars. A similar phenomenon occurs in eclipsing binaries where the effect of limb darkening on one or both components manifests itself in the shape of the system's light curve.