1) The outer edge or border of the apparent disk of a celestial body.
→ limb brightening, → limb darkening.
From L. limbus "border, hem, fringe, edge," cognate with Skt. lambate "hangs down."
Labé "limb, edge," from lab "lip;" Mid.Pers. lap; cognate with L. labium, E. lip; Ger. Lefze.
Fr.: embrillancement centre-bord
An observed increase in the intensity of radio, extreme ultraviolet, or X-radiation from the Sun from its center to its limb.
Fr.: assombrissement centre-bord
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 look 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.
Fr.: bord solaire