Michael Guerrero 1.1 Notes

Chapter 1: Our Place in the Universe

1.1: Our Modern View of the Universe

·         Originally thought to be geocentric, with the Earth as the center of the universe.

A.    What is our place in the universe?

a.       Earth is a planet within a solar system with the Sun as the center with other planets as well as asteroids and comets in orbit around.

b.      In the Milky Way Galaxy (relatively large with over 100 billion stars).

c.       Local Groups – Group of about 40 galaxies, one in which contains the Milky Way.

d.      Galaxy Clusters – Groups of galaxies containing more than a few dozen members.

e.       Superclusters – Where galaxies and galaxy clusters are tightly packed.

f.       Universe – The sum total of all matter and energy.

B.     How did we come to be?

a.       Big Bang – 13.7 billion years ago. Universe continuously expanding while galaxies and galaxy clusters do not.

b.      Stars are born when gravity compresses material in a cloud and eventually begins to generate energy through nuclear fusion that creates heavier nuclei by the collision of smaller nuclei. Supernovae releases a majority of star’s material back into space at the end of cycle.

c.       Earliest state of universe contained only the elements of hydrogen and helium, with trace elements of lithium. 4.5 billion years ago, 2% amount of original helium and hydrogen was converted into heavier elements.

C.     How can we know what the universe was like in the past?

a.       Speed of light: 300,000 km/s

b.      Light-year – 10 trillion km or 6 trillion mi/yr

c.       Further the distance, the further back in the past

D.    Can we see the entire universe?

a.       No – looking past 14 billion years extends beyond the boundary of our observable universe, though this does not deny the probability of a universe beyond.