Section #3: The Universe

 Galaxies are large groups of stars dusts and gases held together by gravity.  Our galaxy is the Milky Way galaxy, and it has about 400 billion stars in it.

 The milky way galaxy is a spiral galaxy.  It is 100,000 light years from end to end.  It is 10,000 light years across at its deepest point

 Spiral galaxies have a central concentration of stars with sweeping arms of stars coming from the nucleus.

 Elliptical galaxies have a round to oval shape.  Most elliptical galaxies are small but some of the largest known galaxies are elliptical.

 Irregular galaxies lack a central or consistent shape.  Less than 10% of galaxies are irregular galaxies.

 Galaxies shapes are the most obvious difference between them.  The age of a galaxies stars is however a more important difference.

 Galaxies like stars are grouped in clusters.  This clustering is due to an increased amount of gravity due to the galaxies immense size.

 Remember Doppler Effect…the difference in a way an object looks or sounds due to the direction it is traveling.  Red Shift is a shifting to the long or red end of the visible spectrum due to stars and galaxies motion away from a central point.  This discovery is the leading evidence to support the Big Bang Theory.

 Edwin Hubble is credited with discovering Red Shift.  He also found that a star is shifted farther to the red the faster it moves.  In addition he saw that the farther a star is from us the faster it is moving so….

 …stars farthest from us a re shifted farther to the red.  This idea is called Hubble’s Law.

 The big bang theory states that the universe began as a huge explosion of matter and energy and the universe is continually moving outward from this explosion.

 All matter and energy in the universe was contained in a super dense, hot and massive ball.  The big bang occurred about 13.7 billion years ago hurling the material outward in all directions.

 Theories vary on how the universe will end.  Some believe the energy in the stars will eventually cease causing the stars to burn out like candles one by one.  Others think that the expansion will eventually stop and the immense gravitational contraction will pull every thing back in.