Photosphere
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The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately Page Template:Fraction/styles.css has no content.2⁄3,[1] or equivalently, a depth from which 50% of light will escape without being scattered.
Stars, except perhaps neutron stars, have no solid or liquid surface.Template:NoteTag Therefore, the photosphere is typically used to describe the Sun's or another star's visual surface.
Etymology
The term photosphere is derived from Ancient Greek roots, φῶς, φωτός/phos, photos meaning "light" and σφαῖρα/sphaira meaning "sphere", in reference to it being a spherical surface that is perceived to emit light.Script error: No such module "Unsubst".
Sun's photosphere
The Sun's photosphere has a temperature between Script error: No such module "convert". (with an effective temperature of Script error: No such module "convert".)[3][4] meaning human eyes perceive it as an overwhelmingly bright surface, and with a sufficiently strong neutral density filter, as a hueless, gray surface. It has a density of about 3Template:E kg/m3;[5] increasing with increasing depth.[2] The Sun's photosphere is 100–400 kilometers thick.[6][7]
Photospheric phenomena
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In the Sun's photosphere, the most ubiquitous phenomenon are granules—convection cells of plasma each approximately Template:Cvt in diameter with hot rising plasma in the center and cooler plasma falling in the spaces between them, flowing at velocities of Template:Cvt. Each granule has a lifespan of only about twenty minutes, resulting in a continually shifting "boiling" pattern. Grouping the typical granules are supergranules up to Template:Cvt in diameter with lifespans of up to 24 hours and flow speeds of about Template:Cvt, carrying magnetic field bundles to the edges of the cells. Other magnetically related phenomena in the Sun's photosphere include sunspots and solar faculae dispersed between granules.[8] These features are too fine to be directly observed on other stars; however, stellar spatial structures have been indirectly observed, and can behave like sunspots. We can refer to these as starspots, although clearly non-analogous features also may be present as well.
Notes
References
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External links
- Page Template:Sister-inline/styles.css has no content.Script error: No such module "Sister project logo". Media related to Script error: No such module "Commons link". at Wikimedia Commons
- Animated explanation of the Photosphere Script error: No such module "webarchive". (University of South Wales).
- Animated explanation of the temperature of the Photosphere Script error: No such module "webarchive". (University of South Wales).
- Solar Lower Atmosphere and Magnetism (MPS)
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