The Universe Ch. 20

 d. universe: the sum of all space, matter & energy for all time (past, present, & future)   Mostly empty space! What is the universe?

 It all started in a small, concentrated place  ~13.8 billion years ago  Has been expanding ever since  Gravity clumped thing together  What was formed from those clumps of cosmic stuff? Big Bang Theory

 d. star: ball of gas that emits (gives off) EMR (electromagnetic radiation)  driven by nuclear fusion  hydrogen nuclei combined into helium  HUGE energy output What is a star?

 Classified by size  Supergiant (Rigel, Betelgeuse)  Giant  Medium-sized (Sun)  White dwarf  Neutron (16 km; about the size of Manhattan island)

 Elements…but how do we know which ones?  Color  Indicates temp of star (NOT size!)  R O Y G B I V  Cooler to hotter What are they made of?

 Spectroscope  tool to see light spectra (“rainbows”)  Spectral lines – each element gives off different pattern of colored light  Each pattern is unique to a specific element

What’s out there?  Mostly empty space  Superclusters  Clusters  Galaxies  Stars  Planets & stellar systems  Gas, dust, smaller stuff BIG little

 d. cluster: a group of stars & galaxies bound by gravity  Local group  Milky Way galaxy (ours!)  Andromeda galaxy (closest to us)  Hercules cluster (p. 675) SNICKERS

 d. galaxy: a collection of stars, gas, & dust held together by gravity  Millions or billions of stars  So far away that we can’t see individual stellar systems  Newer galaxies appear bluish  Older galaxies appear reddish

 Classified by shape  Spiral  Elliptical (not quite circular)  Irregular Messier 74 Great Barred