The Habitable ZoneThere are approximately seven billion people living on Earth right now. Who can imagine 1 million people, let alone 7 billion people? But the total misunderstanding of this does not make the fact any less true. No one has ever seen an alien or an organism that is not native to Earth, but that doesn't make the prospect any less valid. Most citizens of Earth can't imagine living anywhere other than on this blue planet, but that shouldn't make the possibility any less real. Space, like the future, is always before us and no one can predict what it holds for us or what ideas we will find. Outside of Earth, life in the universe is not as foolish a thought as once believed. First, there are a number of variables that influence the habitable zone of stars. There are also an insurmountable number of possibly habitable planets that could harbor life. Finally, evidence of life in space has been found, although the evidence is scarce. IN 1953, Hubertus Strughold and Harlow Shapley were the first to mention the habitable zone, although the term they used was "Liquid Water Belt" (Handover). Simply put, the definition of a habitable zone is the distance from a host star that a planet must reach to maintain liquid water (Palmer). To calculate the HZ length of a star, you need variables such as the planet's brightness, temperature, solar irradiance, and distance from the sun. ("Habitable zone"). Because Earth has such large quantities of H2O, it's not unreasonable to think that everywhere is the same, but that's actually not the case. Unbeknownst to some, water is actually the hottest commodity in the universe. A planet must be within a HZ to support water and subjectively to support complex life If a planet is…half of the paper…e.g. September 4, 2003. Web. .Townsend, Rich. "Life in the solar system: Mars, Europa and Titan". Mad Star - February 27, 2014. "Water and climate" Web. Boehm, Sven. "Early Christmas present for the Kepler mission: first Earth-sized planet in a habitable zone around a Sun-like star now confirmed - Institute for Theoretical Astrophysics 9 December 2011. Web. Böhm., Sven. "Life on Gliese 667Cc ?" - Institute of Theoretical Astrophysics 28 August 2013. Web. 2014. .