AST 301 Lecture Notes - Lecture 29: Thermostat, Photosphere, Radiation
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Maintained by gravity pushing in on the star and pressure from fusion pushing out. If hyd(cid:396)ostati(cid:272) e(cid:395)uili(cid:271)(cid:396)iu(cid:373) e(cid:374)ded the su(cid:374)"s size would (cid:272)ha(cid:374)ge. Hydrogen is converted to helium in the core through nuclear fusion. The a(cid:272)t of (cid:272)ha(cid:374)gi(cid:374)g a(cid:374) ele(cid:373)e(cid:374)t i(cid:374)to a(cid:374)othe(cid:396) (cid:271)y a (cid:396)ea(cid:272)tio(cid:374) (cid:271)etwee(cid:374) the ele(cid:373)e(cid:374)t"s (cid:272)o(cid:396)es. High temperature and high pressure is needed; this is why it is done in the core. Core temperatures lowering causes fusion to slow down, so the star contracts and heats up. Core temperatures rising causes fusion to speed up, the core expands and cools down. A temperature of millions of kelvin and high density. The density would decrease, and fusion would slow down, releasing less energy. In the outer layers of the sun energy flows out by convection. Photosphere: layer where visible light is emitted. The sun appears darker around the edges because it is cooler and glows less bright. Sunspots are darker because they are cooler than their surroundings.
