 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

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

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

 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

 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

 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 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

 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

 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

 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