limb brightening

limb brightening

The increase in intensity at X-ray and radio wavelengths from the center to the limb of the Sun's disk. It arises at radio wavelengths for the same reason as the limb darkening at visible wavelengths but has the opposite effect, because the radiation is emitted from the high-temperature upper chromosphere/inner corona rather than from the photosphere. At X-ray wavelengths, where the material is less opaque, intensity is determined by path length rather than radiation temperature.

limb brightening

[′lim ‚brīt·ən·iŋ]
(astronomy)
An observed increase in the intensity of radio, extreme ultraviolet, or x-radiation from the sun or another star from its center to its limb.
References in periodicals archive ?
Therefore one would expect limb brightening even in the absence of temperature increase, simply due to the secant increase of path length.
Given the dusty and misty conditions early in the present apparition, I suspect that the east and west limbs of Mars will display limb brightening (also called limb arcs) caused by scattered light from dust and dry ice particles high in the Martian atmosphere.