Astronomy Answers: From the Astronomical Dictionary

Astronomy Answers
From the Astronomical Dictionary

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The description of the word you requested from the astronomical dictionary is given below.

the penumbra

paene = [Latin] almost; umbra = [Latin] shadow

The penumbra is the outermost part of a sunspot, in which thread-like light and dark filaments mostly point away from the umbra. These structures are formed by strong magnetic field.