Page 28 - Curriculum Visions Dynamic Book

Granulation
Penumbra
Umbra
Sunspots are dark features in the upper photosphere. Because dark indicates cool, sunspots are places where the full upward-flowing energy of the Sun is blocked.
Sunspots are formed by convection currents but on a different scale than granulation. They are often thousands of kilometres across and are also closely connected with the Sun’s magnetic field. Wherever a sunspot occurs, the magnetic field is preventing the normal amount of convection. As a result, hot materials do not reach the surface as quickly, and so the surface is cooler by about 1,500°C, and therefore darker, than the surroundings.
From this core the magnetic field then spreads out across the spot. The shape of a sunspot is often like an open flower, with a dark central region (called the umbra) surrounded by a ring of dark “petals” called the penumbra.
 This diagram is a closeup view of a moderately large sunspot. The field of view covers about 60,000 km horizontally and
38,000 km vertically. The diameter of this sunspot is about 16,500 km; the Earth, with an equatorial radius of 6,378 km, would cover up the very dark region (called the umbra) but not the medium-dark region (the penumbra). Sunspots can be quite small (1,500 km diameter) or reach sizes up to 50,000 km.
Sunspots last for weeks and months, then break up into smaller and smaller sunspots.
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