Part of a large sunspot,
recorded on 15 July 2002
with the Swedish 1-m Solar
Telescope on La Palma. The
centre of the sunspot, known
as the umbra, appears dark
because strong magnetic
fields there stop hot gas
upwelling from the solar
interior. The penumbra,
surrounding the umbra, is
made up of thread-like
structures.The
Sun
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