Basic Structure of the Sun

Basic Structure of the Sun - convection from radiative zone...

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Basic Structure of the Sun For this course we only look at the basic structure of the Sun (there are other courses at UCL dealing with Solar Physics) in order to understand where the solar wind comes from. You can get further information on the Web. Details of NASA's "Roadmap" for research into Sun-Earth connections, for example, can be found on this link. The Sun is a "standard" G2 type star, unremarkable in most senses. It is largely gaseous, though the gases composing it are mostly at immense pressure and temperature. It does not rotate as a solid body, though the inner and outer parts are "coupled" by convective and radiative transfer. The main parts of the Sun's structure are: The core, where fusion occurs of Hydrogen to form Helium - temperature around 15 10 6 K Radiation zone - out to about 70% of the Sun's radius. The temperature falls with radius down to c. 1.5 10 6 K Convection zone - as the atmosphere becomes more opaque it cannot sustain the intensity of radiation needed to transfer the heat so the large temperature gradient has to be maintained by
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Unformatted text preview: convection from radiative zone to photosphere Photosphere - the "visible" surface of the sun c 6000K Chromosphere - above the photosphere, the temperatsphere, the temperature drops away from the surface to c 4500K and then rises to 8500K. Because it is initially cooler that the photosphere below it, it is marked by the presence of absorption lines in the solar spectrum - particularly the main transitions in the Hydrogen atom like the Lyman and Balmer lines. Noted particularly for H-alpha at 656.3nm Corona - from a process still not completely understood, the "atmosphere" above the chromosphere is heated to temperatures around 10 6 K - this region is the corona. The chemical composition of the upper solar atmosphere is variable and different from that of the surface layers of the Sun. Magnetic field - the sun's magnetic field is generated by dynamo action, though the details are still not entirely understood....
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