Chapter 1 ± Our Place in the Universe
Our Place in the Universe
x Earth is a planet in out solar system, which consists of the Sun and all the objects that
orbit it, which include the planets and their moons, chunky rocks of asteroids, icy balls
of comets, and particles of interplanetary dust.
x Our Sun is a star; the Milky Way Galaxy is a huge disk-shaped collection of stars
(containing more than 100 billion stars).
x A galaxy is a great island of stars in space, containing from a few hundred million to a
trillion or more stars.
x Our solar system is located a little over halfway from the galactic center to the edge of
the galactic disk.
x Local Group is groups of galaxies.
x SuperClusters are galaxies and galaxy clusters that are tightly packed.
x Our local group belongs to the local Supercluster.
x The universe is the sum total of all matter and energy, encompassing the superclusters
and voids and everything within them.
Our Cosmic Address:
The Big Bang and the Expanding Universe
x Telescopic observations of distant galaxies show that the entire universe is expanding
Æ average distances between galaxies are increasing with time.
x Estimation that the expansion started about 14 billion years ago Æ called the Big
x While the universe as a whole continues to expand, individual galaxies and their
contents do not expand.
x As the universe grows larger, the matter within it tends to clump into galaxies and
galaxy clusters, forming our own Milky Way a few billion years after the Big Bang.
Stellar Lives and Galactic Recycling
x Gravity drives the collapse of clouds of gas and dust to form stars and planets.
clouds of gas and dust and then shine for millions or billions of years.
x The energy that induced the shining is nuclear fusion LQWKHVWDU¶VFRUHÆ the
process where lightweight atomic nuclei smash together and stick/fuse to make
heavier nuclei. Finally, a star ³dies´ when it exhausts all its usable fuel for fusion.
x :KHQDVWDU³GLHV´LWH[SORGHVsupernovae), blowing out its content back into space.
The returned matter mixes with other matter floating between the stars in the galaxy,
eventually becoming part of new clouds of gas and dust from which new generations
of stars can be born.