AST101H1 Chapter Notes - Chapter 1: Galactic Center, Observable Universe, Edwin Hubble

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Published on 10 Oct 2012
School
UTSG
Department
Astronomy & Astrophysics
Course
AST101H1
Professor
September 19, 2011
Chapter One: Our Place in the Universe
1.1 Our Modern View of the Universe
- Earth is a planet in our solar system
- The sun and all the stars we can see with the naked eye make up only a small part of a
huge, disk-shaped collection of stars called the Milky Way Galaxy (more than 100
billion stars)
- A galaxy is a great island of stars in space, containing from a few hundred million to a
trillion or more stars
- Milky Way is one of the two largest among about 40 galaxies in the Local Group
- Groups of galaxies with more than a few dozen members are often called galaxy clusters
- The regions in which galaxies and galaxy clusters are most tightly packed are called
superclusters
- The universe is the sum total of all matter and energy, encompassing the superclusters
and voids and everything within them
- Expansion of universe occurred about 14 million years ago
- The point at which the expansion of universe began is called the Big Bang
- Other chemical elements were made by stars
- While the universe as a whole continues to expand, individual galaxies and galaxy
clusters do not expand
- A star is born when gravity compresses the material in a cloud to the point where the
center becomes dense enough and hot enough to generate energy by nuclear fusion, the
process in which lightweight atomic nuclei smash together and stick to make heavier
nuclei
- A star lives as long as it can shine with energy from fusion, and dies when it exhausts its
usable fuel
- In its final death throes, a star blows much of its content back out into space
- Massive stars die in titanic explosions called supernovae
- The early universe contained only the simplest chemical elements: hydrogen and helium
- Elements such as carbon, nitrogen, oxygen were manufactured by stars
- Most of the material from which we and our planet are made was created inside stars that
lived and died before the birth of the sun
- Early solar system was made of about 98% hydrogen and helium and 2% other elements
- Speed of light is 300,000 km per second
- Light takes 1 second to reach Earth from the moon, and about 8 minutes to reach Earth
from the sun
- One light-year is the distance that light can travel in 1 year about 10 trillion kilometers,
or 6 trillion miles
- A light-year is a unit of distance, not time
- The Orion Nebula is a giant cloud in which stars and planets are forming. It is located
about 1500 light-years from Earth
- Our universe is about 14 billion years old
- Observable universe the portion of the entire universe that we can potentially observe
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Document Summary

Earth is a planet in our solar system. The sun and all the stars we can see with the naked eye make up only a small part of a huge, disk-shaped collection of stars called the milky way galaxy (more than 100 billion stars) A galaxy is a great island of stars in space, containing from a few hundred million to a trillion or more stars. Milky way is one of the two largest among about 40 galaxies in the local group. Groups of galaxies with more than a few dozen members are often called galaxy clusters. The regions in which galaxies and galaxy clusters are most tightly packed are called superclusters. The universe is the sum total of all matter and energy, encompassing the superclusters and voids and everything within them. Expansion of universe occurred about 14 million years ago. The point at which the expansion of universe began is called the big bang.

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