Stars are grouped into pictures in the sky called constellations. Northern hemisphere constellations origin from ancient greeks: named after animals and mythological characters (queen, bull, hunter) Southern hemisphere constellations named due to voyagers by explores: modern names (telescope, microscope, air pump) Tool for navigation: polaris: north star, easy to find, directly above north pole, facing polaris facing north. Used for agriculture: different constellations in summer vs. winter (triangle) Stars that appear close in sky may not be close in space: not all same distance. Brightest star in constellation named greek alphabet: brightest = alpha, 2nd = beta, 3rd = gamma. Stars seem to be on the inner surface of a sphere surrounding earth: they aren"t, use 2 dimensional spherical coordinates to locate sky objects. North celestial pole (ncp: directly above earth"s north pole. Celestial equator (ce: directly above earths equator. South celestial pole (scp: directly above earths south pole.