- In astrophysics, the gradual decrease in observed brightness of the disk of a star from its centre to its edge (limb).This phenomenon, readily apparent in photographs of the Sun, occurs because the solar atmosphere's temperature increases with depth. Looking at the Sun's centre, an observer sees the deepest, hottest layers, which emit the most light. At the limb, only the upper, cooler layers, which produce less light, are visible. Observations of solar limb darkening are used to determine the temperature structure of the Sun's atmosphere.
* * *in astrophysics, gradual decrease in brightness of the disk of the Sun or of another star as observed from its centre to its edge, or limb. This phenomenon is readily apparent in photographs of the Sun. The darkening is greatest for blue light, amounting to a drop of as much as 90 percent from the Sun's photosphere to its outer atmospheric regions. Such limb darkening occurs because the solar atmosphere increases in temperature with depth. At the centre of the solar disk, an observer sees the deepest and warmest layers that emit the most light. At the limb, only the upper, cooler layers that produce less light can be seen. Observations of solar limb darkening are used to determine the temperature structure of the Sun's atmosphere. Information derived from such observations is applied in studying other stars.
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