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chapter 1

Astronomy & Astrophysics
Course Code
Clifford Orwin

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!!!! Our place in the Universe(Chapter 1)
Geocentric - Cannot feel the constant motion of Earth as it rotates on its axis and orbits
the sun
Cosmic Address - Our place in the universe
Solar System (e.g.. Earth) - Consist of the sun and all the objects that orbit it (planets,
their moons and smaller objects including rocky asteroids and icy comets).
Milky Way Galaxy - disk shaped collection of stars (100 billion stars)
-1 of the 2 largest among the 40 galaxies in the LOCAL GROUP
Galaxy - island of stars (few 100 million to trillion or more stars)
Galaxy Clusters - galaxies with more than a few dozen members (very dense)
-arranged in giant chains with huge voids between them
SuperClusters - area where galaxies and galaxy cluster are most tightly packed
Asteroid - small rocky object that orbits a star. Part of a category called “small solar
system bodies”
Comet - Small ice rich object that orbits a star. Part of a category called small solar
system bodies”
-Our solar system is located a little more than halfway from the galactic center to the
edge of the galactic disk.
Definition of of OUR UNIVERSE:
-Sum total of all matter and energy, encompassing the supercluster and voids and
everything within them.
Our Place in the UNIVERSE:
-We live on a planet orbiting and avg. star among more then 100 billion stars in the
Milky Way Galaxy.
Big Bang (the rate at which galaxies are moving apart) and Expanding Universe
-The Universe is expanding----the avg. distance between galaxies is increasing in time
-Expansion began 14 billion years ago
-Force of gravity has drawn matter together causing matter within to clump together
resulting into galaxies and galaxy clusters
Stars and planets are formed by:
-collapse of clouds of gas and dust
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