2.  Stars are born from great clouds of gas and dust  They mature, grow old, and die  The more massive a star is, the shorter its life  A star is a sphere of super-hot gases – mostly hydrogen and helium  Vary greatly in their masses, size and density

3.  The range of colors a star emits depends on its surface temperature.  Cool stars  redder in color  Stars 3900-7000 degrees C  yellow  Stars 7000-9500 degree C  white  Stars 9500+ degrees C  blue

5.  Diagram that pictures the life of a star  Classifies stars based on temperature and luminosity

6.  Majority of stars (about 90%) fall in this category  Runs from upper left (high luminosity, high surface temperature ) to lower right (low luminosity, low surface temperature)  Life span: 1 million – 1 billion yrs  Actively fuse hydrogen and helium  Example: our Sun

7.  Closest star to Earth  Middle aged star  predicted to keep shining for 5 billion more years  Diameter: 870,000 miles wide  If the sun were hollowed, you could fit 330,000 Earths inside  Core Temperature: 27 million degrees Fahrenheit  Made out of mostly hydrogen

8.  Most stars are red dwarfs  Stars with less than 50% the mass of the sun  1/10,000 th the energy of the sun  It is estimated there are between 200-400 billion stars in our galaxy  The closest star to Earth, besides the sun is Proxima Centauri – located 4.2 light years away  On the fastest spacecraft, it would still take 70,000 yrs to get there

9.  Greater luminosity than main sequence stars  Star is moving toward end of life  Helium sinks to the center of the core  Raises star’s temp.  Outer shell begins to swell

10.  Beginning of star shedding its outer layer  Becomes a small, dense body  Cools for billions of years and eventually becomes dark and produces no energy

11.  A few stars do not follow the evolutionary path and go out with a bang  Violent explosion that leaves behind a small core known as a neutron star  If the remnant is large enough = black hole