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Lecture 18

# AST 101 Lecture Notes - Lecture 18: Atomic Nucleus, Current Source, Red Giant

Department
Astronomy
Course Code
AST 101
Professor
Walter Freeman
Lecture
18

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The\$Sun
We’ve\$explained\$the\$solar\$spectrum\$now:
temperature
the\$cooler\$gases\$in\$the\$Sun’s\$atmosphere\$absorb\$those\$wavelengths\$
corresponding\$to\$their\$energy-level\$transitions,\$giving\$rise\$to\$the\$missing\$
wavelengths\$(dark\$lines)\$in\$the\$spectrum
But\$why\$is\$the\$Sun\$so\$hot?\$What’s\$the\$source\$of\$the\$Suns\$energy\$in\$the\$first\$
place?
Nuclear\$fusion
smaller\$ones.
terrific\$pressure,\$that\$all\$of\$the\$electrons\$are\$torn\$off\$of\$their\$atoms;\$for\$this\$discussion,\$
are\$just\$single\$protons.
As\$you\$know,\$protons\$are\$positively\$charged.\$Since\$like\$charges\$repel,\$if\$two\$protons\$
get\$near\$each\$other,\$they\$will\$violently\$repel\$each\$other.\$It\$takes\$a\$tremendous\$amount\$
of\$heat\$and\$pressure\$to\$overcome\$this.\$However,\$this\$amount\$of\$heat\$and\$pressure\$is\$
found\$in\$the\$heart\$of\$the\$Sun,\$where\$the\$temperature\$reaches\$15\$million\$Kelvin\$(or\$
Celsius).
So,\$what\$happens\$if\$you\$smash\$together\$two\$protons\$hard\$enough?\$Well,\$if\$you\$can\$
overcome\$the\$electric\$ repulsion\$and\$bring\$them\$very\$close\$together,\$then\$there\$is\$
an attractive nuclear\$force\$that\$will\$then\$hold\$them\$together.\$In\$the\$process,\$one\$of\$
them\$changes\$to\$a\$neutron\$(absorbing\$an\$electron\$in\$the\$process).\$This\$gives\$us\$a\$new\$