How many stars are there in the Milky Way galaxy anyway?  Answer: 250 – 500 billion (well, ± 150 billion or so).  That’s a lot of stars and the Sun is just one of them.  Among many astronomers, it is generally accepted that there is, on average, at least one planet per star.  What astronomers are really looking for is a habitable planet, with abundant water, about the size of the Earth orbiting a star about the size of our Sun.  When you’re dealing with 250 billion, well, there just must be more than just one.  Right?  What if 18% of Sun-like stars had an Earth-like planet?  That would mean there are up to six billion Earth-like planets in the Milky Way galaxy alone.  That’s the latest estimate from astronomers at the University of British Columbia where they made an extrapolation based on NASA’s Kepler space telescope.  Just think about that. . .
 
So, What Are “Intelligent” Civilizations, Exactly?
 
Any intelligent civilization is generally one with the ability to use a written language and possess advances in the arts and sciences.  Bear in mind that these scientists are not just referring to spacefaring civilizations with a fleet of starships at hand.  They are referring to any carbon-based (perhaps even silicon-based) beings with the ability to reason, understand, perceive relationships and to communicate in a technical manner.  The cosmologists are describing what are called “technologically-advanced” civilizations that have invented radio technology and have been broadcasting via radio, TV or by any other means into space.   
 
Thirty-six Intelligent Civilizations
 
Published on June 15 in The Astronomical Journal, a paper titled “The Astrobiological Copernican Weak and Strong Limits for Intelligent Life” 2 estimated that there are roughly “36 civilizations within our Galaxy.”  The paper was written by Tom Westby, Assistant Professor of Engineering, and Christopher Conselice, Professor of Astrophysics, at the University of Nottingham (UK).  But let’s be clear, the paper’s authors  claim that that number could be as high as 210 and as few as four civilizations, depending on their assumptions (that’s where the “strong” scenario and the “weak” scenario come into action).  Their paper is limited only to Earth/Sun-like star systems, and that’s why the word “Copernican” is used in the title.

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