Sunspots
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A hole in the Sun (2/2)
Swedish 1m Solar Telescope
A sunspot is a huge concentration of magnetic field seen on the solar surface, in the layer of the Sun called photosphere. The photosphere is the visible surface of the Sun, from which most of the Sun’s light that reaches Earth directly is emitted. Embedded in this surface (which is not a solid surface) one can see from time to time huge dark features that move across the solar disk, relatively close to the solar equator. Since they are embedded in the surface, sunspots follow the Sun's rotation. The magnetic field in these concentrations can reach values up to 6000 Gauss. Their size span as much as 50000 km for a single sunspot (and sometimes they group together). Several Earths could fit inside one of those monsters!
The beautiful sunspot we see in these images was observed close to disk center on July 2, 2010 with the Crisp Imaging Spectropolarimeter at the Swedish 1-m Solar Telescope. The images were recorded in the continuum of the calcium H line and in the H-alpha 6563 Å line center, which show two different heights in the solar atmosphere. The sunspot has two differentiated parts, an umbra (darker) and a penumbra (brighter and full of filamentary structure). In the umbra the magnetic field is vertical, while it bends in the penumbra becoming horizontal at the edge of the sunspot. The H-alpha image is looking further up in the atmosphere, and one can literally see the magnetic field lines coming out of the sunspot. We "see" them because plasma gets trapped in them and trace their existence. All sort of waves escape from the interior of the sunspot and travel upwards.
Image credit: Mats Carlsson, Viggo Hansteen, Luc Rouppe van der Voort (ITA, University of Oslo)
Text credit: Ada Ortiz (ITA, University of Oslo)