In order to more easily locate objects in the sky, we divide the sky into regions named after familiar patterns of stars called constellations . Ancient constellations were imaginary pictures outlined by familiar patterns of stars (stick figures). Modern astronomers divide the sky into 88 official constellations or regions of space, many of which contain the ancient star patterns.
Sphere image of Constellation Boundaries
12 Constellations (traditional) along the ecliptic
Pisces, Aries, etc.
North and South
Never setting (N), or never rising (S)
In north, appear to wheel eternally about Polaris, the North Star
RA & Dec http://abyss.uoregon.edu/~js/ast122/lectures/lec02.html
Summary Earth Globe Celestial Sphere North Pole North Celestial Pole South Pole South Celestial Pole Equator Celestial Equator Prime Meridian Vernal Equinox Latitude Declination Longitude Right Ascension
Coordinate system based upon an observer’s horizon, not the celestial equator
Horizon-”Straight ahead”, line where earth and sky appear to meet
Zenith-point straight up
Meridian-Line “due south”, passes from north horizon through zenith to south horizon
Nadir-point straight down
Horizon System Diagram http://www.yorku.ca/phall/P1070W05/L04/bea02-05.jpg