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The photosphere is the visible "surface" of the Sun (left). Sunspots are often visible "on" the photosphere. A close-up view (right) shows the granulation pattern on the photosphere.
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Images courtesy of SOHO/NASA/ESA and The Royal Swedish Academy of Sciences and Oddbjorn Engvold, Jun Elin Wiik, and Luc Rouppe van der Voort - University of Oslo.

The Photosphere - the "Surface" of the Sun

Most of the energy we receive from the Sun is the visible (white) light emitted from the photosphere. The photosphere is one of the coolest regions of the Sun (6000 K), so only a small fraction (0.1%) of the gas is ionized (in the plasma state). The photosphere is the densest part of the solar atmosphere, but is still tenuous compared to Earth's atmosphere (0.01% of the mass density of air at sea level). The photosphere looks somewhat boring at first glance: a disk with some dark spots. However, these sunspots are the site of strong magnetic fields. The solar magnetic field is believed to drive the complex activity seen on the Sun. Magnetographs measure the solar magnetic field at the photosphere.

Because of the tremendous heat coming from the solar core, the solar interior below the photosphere (the convection zone) bubbles like a pot of boiling water. The bubbles of hot material welling up from below are seen at the photosphere as slightly brighter regions. Darker regions occur where cooler plasma is sinking to the interior. This constantly churning pattern of convection is called the solar granulation pattern.


Last modified January 12, 2010 by Randy Russell.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA