Sunspots
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Sunspot in AR 11302
Swedish 1-m Solar Telescope
This continuum intensity image shows a relatively simple circular sunspot in active region 11302. It was observed on September 28, 2011 with the CRISP instrument at the Swedish Solar Telescope on La Palma, when the spot was very close to the disk center. The observations were made in the Fe I 6173 Å line, which is formed in the photosphere.
Sunspots are magnetic structures on the surface of the Sun. They consist of a dark nucleus called the umbra and a brighter region surrounding it - the penumbra. Sunspots harbor the strongest fields occurring in the solar atmosphere (up to 3000-6000 G).
The umbra appears dark because energy transport by convection is inhibited by the strong magnetic field. However, it is not suppresed entirely. In the penumbra, convection takes place in elongated convective cells oriented in the radial direction, following the general organization of the penumbral magnetic field.
Both the umbra and the penumbra of sunspots show incredible fine structure and dynamics, with typical sizes below 100 km. These scales are barely resolved with current telescopes.
Image credit: Sara Esteban Pozuelo (IAA-CSIC), Luis Bellot Rubio (IAA-CSIC), Ada Ortiz (ITA, University of Oslo)
Publication: Esteban Pozuelo et al., 2015, ApJ, 803, 93