facula

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facula
1. A brighter and hotter patch on the Sun's photosphere, visible in white light and best seen near the solar limb against the background of limb darkening. Faculae often appear shortly before a sunspot group forms, and remain visible for several days or weeks after the spots have vanished. High-latitude (polar) faculae also occur, well away from sunspots; these, unlike sunspot faculae, are most numerous on the rising part of the sunspot cycle. Faculae are slightly hotter (by about 300 K) than the surrounding photosphere. They are locations of strong magnetic fields (0.1 tesla), and coincide with bright patches in the chromosphere (plages) and the chromospheric network. Normally they can be resolved into small facular bright points, around 150 km wide, lasting 20 min or so. There is often a connection between faculae and structure within large sunspots, in particular light-bridges, which are ridges of bright material crossing a sunspot.

2. A bright spot on a planetary surface; pl.faculae. The name is not a geological term, but is used in the nomenclature of individual features, for example Memphis Facula on Ganymede.

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