Chapter 2 - discovering the sky (sept. 12) Stars in a constellation may not be close to each other in space - just appear grouped from earth (star charts on p a-28 to 31 in appendix 1) Constellations serve as a background used to detect the motions of solar system objects. Our location on earth determines our horizon, zenith and meridian. Minute of arc - 1" = 1 degree / 60. Second of arc - 1 = 1" / 60 = 1 degree / 3600. We see the angle of an object. That angle depends on its distance from us. Cosmic calculation with angles angular size / 360 degrees = diameter / circumference=2pi x distance. We measure angular size and distance, solve for diameter diameter = angular size x 2pi x distance / 360 degrees. Earth"s counterclockwise rotation causes all astronomical objects to appear to rise/set every day.