Limb darkening
![An image of the Sun in visible light showing the limb-darkening effect as a drop in intensity towards the edge or limb of the solar disk. The image was taken during the 2012 transit of Venus (seen here as the dark disk at the upper right).](/Images/godic/202501/24/2012_Transit_of_Venus_from_SF1347.jpg")
![An idealized case of limb darkening. The outer boundary is the radius at which photons emitted from the star are no longer absorbed. L is a distance for which the optical depth is unity. High-temperature photons emitted at A will just barely escape from the star, as will the low-temperature photons emitted at B. Note that for a typical star, this drawing is not to scale. E.g., for the Sun, L would be only a few hundred km.](/Images/godic/202501/24/Limb_darkening_layers.svg1347.png")
![](/Images/godic/202501/24/Limb_darkening_geometry.svg1347.png")
Limb darkening is an optical effect seen in stars (including the Sun), where the center part of the disk appears brighter than the edge or limb of the image. Its understanding offered early solar astronomers an opportunity to construct models with such gradients. This encouraged the development of the theory of radiative transfer.