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Sun: Accounts for 99.86% of solar system’s total mass. Made mostly of hydrogen and helium gas (2% other). Surface (photosphere – less dense) temp 5800 K. Core temp 15M K. Energy output 3.8x10^26 Watts. Generates energy from nuclear reactions in core. Fission: Big atomic nucleus splits into smaller pieces (power plants) Fusion: Small atomic nuclei combine, make bigger nuclei (Stars).Hydrogen Fusion: Sun releases energy by fusing 4 H nuclei into 1 He nucleus. 10^38 per sec. Needs high temp, speeds and densities for repelling nuclei to get close enough for strong nuclear force to act. Fusion only in hot/dense enough core. Produces Neutrinos: hard2 detect, pass through matter, escape Sun immediately. Neutrino Telescope to detect from solar fusion (# of detected n is small).Sun’s Energy: At centertemp hot, gas translucent, energy moves by radiation (photons). At surfacegas opaque, energy moves by convection. Photosphere shows convection granules (1000 km across): Hot gas rising (brighter), cool gas falling (darker). -Hot, opaque objects emit thermal radiation. Light has spectrum depending on object’s surface temperature. Spectral curve has wavelength (color) on x axis, intensity (energy output/second) y axis. Hotter objects emit more light per unit surface area. The hotter an object, the shorter the wavelength of its maximum output. The color of thermal radiation can tell us temperature. Bluer = hotter. Sun Atms: 1. Photosphere– “surface”, 500km thick, avg. temp 5800K 2. Chromosphere– lower atms, 1000x fainter than photosphere, temp: 45---500000K 3. Corona– Outer atms, temps up to 2000000K, very faint. 2&3 visible only during eclipse.Active Sun: Disruptions connected to each other/Sun’s magnetic field. 11 yr period, disrupts cmn, satellites, electric power generationSunspots– darker regions of photosphere (cooler than rest of surface). Not permanent, last few days to weeks, form in groups, change over time. Regions above (chromo, corona) bright, alive with activity. Result of magnetic fields suppressing convection, preventing surrounding plasma from sliding into sunspot. Rise/fall 11 year cycle (really 22). Sun rotates fast at equator, slow at poles. Differentialrotation twists magnetic field. Sunspots: loops in tangled field poking through surface. Field reorders at end of cycle, north/south flip. Prominences – Magnetic lops can extend up to corona. Gas from chromosphere trapped in loops. Cooler/denser than surrounding corona. Twisting motion of material.