ASTR 111 Chapter Notes - Chapter 1.2 - 1.4: Solar System, Cosmic Calendar, Milky Way
8 Sep 2017
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Cosmic recycling plants only 2 elements: hydrogen and helium, others were recycled. Many generations of stars have lived and died in the milky way galaxy. Solar system born 4. 5 billion years after big bang 2% of hydrogen and helium had been converted to heavier stuff. Individual galaxies and galaxy clusters do not expand. Gravity drives collapse in which two (or more) smaller nuclei slam together to make larger nucleus. Most massive stars die in titanic explosions called supernovae. Returned matter mixes with other matter floating between the stars in galaxy, eventually becoming part of new clouds of gas to form new stars. Others through nuclear reactions accompanying explosions that end stellar lives. In summary, most material from which we and our planet are made was created by stars that lived and died before the birth of our sun. On cosmic calendar, human existence only falls into the last half-minute. We are being spun in circles as earth rotates.
