Galaxy NGC 4414 , a typical spiral galaxy in the constellation Coma Berenices , is about 55,000 light-years in diameter and approximately 60 million light-years away from Earth. A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants , an interstellar medium of gas and dust , and an important but poorly understood component tentatively dubbed dark matter .   The word galaxy is derived from the Greek galaxias (γαλαξίας), literally "milky", a reference to the Milky Way galaxy. Examples of galaxies range from dwarfs with as few as ten million (10 7 ) stars  to giants with a hundred trillion (10 14 ) stars,  each orbiting their galaxy's own center of mass . Galaxies contain varying amounts of star systems , star clusters and types of interstellar clouds . In between these objects is a sparse interstellar medium of gas, dust, and cosmic rays . Dark matter appears to account for around 90% of the mass of most galaxies. Observational data suggests that
This is the end of the preview. Sign up
access the rest of the document.
This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.