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Chapter 1

Astronomy 1021 Chapter Notes - Chapter 1: Usable Fuel, Big Bang, Observable Universe


Course Code
ASTR 1021
Carol Jones

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September 12, 2011
Chapter 1-Our Place in the Universe
What is Our Place in the Universe?
Solar System- A star and all of the objects that orbit around it
The planets and their moons as well as asteroids and
comets orbiting
around the sun.
Galaxy- A great island of stars in space, containing from a few
hundred million to a trillion or more stars bound together by gravity.
Milk Way Galaxy- Huge, disk-shaped collection of more then 100
million stars
Local Group- The group of approximately 40 galaxies to which Milky
Way Galaxy belongs.
Cluster of Galaxies- A collection of a few dozen or more galaxies
bound together by gravity
Group of Galaxies- A few to a dozen galaxies bound together by
Supercluster- The region in which galaxies and galaxy clusters are
most tightly packed. (Clusters of galaxy clusters)
Universe- The sum total of all matter and energy, encompassing the
superclusters and voids and everything within them.
How did We Come to Be?
The big bang is the point when expansion began, 14 million years
The entire universe is still expanding while gravity pulls matter
together to make galaxies. The average distance between galaxies is
increasing with time.
The early universe contained only two chemical elements (hydrogen
and helium). Other elements were made by stars and recycled from
one stellar generation to the next within galaxies.
1) Gravity compresses material in a cloud to a high enough density
and heat that there is enough energy to generate nuclear
fusion, the process in which lightweight atomic nuclei smash
together to fuse to make heavier nuclei.
2) Stars live as long as it can shine with energy from nuclear fusion.
3) Stars die when the usable fuel is used up.
Early universe only contained hydrogen, helium and a trace of lithium.
Elements were created by:
the nuclear fusion that makes stars shine
through nuclear reactions accompanying the explosions that end
stars’ lives
Discovering the historical universe
Looking at light from distant stars and galaxies is looking into the past
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