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Unformatted text preview: FREQUENTLY ASKED QUESTIONS February 13, 2012 Content Questions What exactly does metallicity for a star mean? Astronomers call any element with Z 3 a metal, whether or not it really can exist in metallic form. Astronomers use the word metallicity to mean fractional composition of elements with Z 3. Stars with high metallicity might have more than a few percent of such elements in their composition. What are those three surfaces in the Sun? The surface of the Sun from our observational point of view is the pho- tosphere: this is the surface of last scattering of most of the photons we see in visible light. Its where the opacity of solar matter to these photons decreases enough that the photons are able to fly to infinity. This layer is quite narrow only 400 km or so so the surface of the Sun appears quite sharp to us. The other surfaces are really layers, with different temperatures, densi- ties and opacities. The chromosphere lies above the photosphere: its hotter, less dense and less opaque. Because its hotter, it can be seen more easily in such wavelengths as UV (those pictures I showed are for shorter wave- length, higher energy photons than visible photons). Above that, the corona is hotter yet, and very tenuous. Could you explain limb darkening?...
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This note was uploaded on 02/26/2012 for the course PHYSICS 105 taught by Professor Kruse,m during the Spring '08 term at Duke.
- Spring '08