ASTR 001 Lecture 20: Astr 1 - Lecture 20
15 Jul 2020
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Document Summary
Earth: diameter 12,800 km or roughly 0. 05 light seconds. Observable universe: 14 billion light years now. Beginning of the universe in big bang. Cosmic microwave background radiation light from the big bang explosion generated radiation, which is still with us today. Just hydrogen (h) and helium (he) atoms. H and he created in the big bang but very little other elements. Some of the h and he gas started to clump into stars. The rst generation stars were made of pure h and he. Typical dying star: h, he, and c, o, fe, and others are ejected into space to form next generation of stars. Our sun made about 4. 5 billion years ago. Death of a massive star (after several million years) i. e. crab nebula 1054 ad. Generations of stars lived and died before our milky way galaxy formed. 10 billion years ago the milky way galaxy formed. Still mostly h and he, but some c, o, and fe, etc.
