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granulation


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A mottling of the Sun's photosphere caused by numerous small light areas called granules. Individual granules are as much as 1000 km across, and may have polygonal shapes. They are separated from each other by darker intergranular lanes, about 400 K cooler than granules. Granule lifetimes are around 20 min, their birth being from the fragments of previous granules and their demise from fragmentation, fading, or sometimes explosion into small fragments. Granules are elongated near sunspots, and also occur within sunspot umbrae (umbral dots). Spectroscopic observations suggest that granules are convection cells of rising hot gas (see convective overshoot), the intergranular lanes marking regions of descending cooler gas.

Subjects: Astronomy and Astrophysics.


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