Stellarium is a free open source planetarium for your computer. It shows a realistic sky in 3D, just like what you see with the naked eye, binoculars or a telescope.
It is being used in planetarium projectors. Just set your coordinates and go.


Its main features include:
Over 120000 stars, all of which are named and explained
Realtime planets with powerful zoom mode
88 constellations
Photorealistic Milky Way
Ground, fog, and landscape
Graphical menu for ease of use
Clickable stars, planets and nebulae with information
Ecliptic and celestrial equator lines
Smooth real time navigation
Windowed and fullscreen modes

This is an absolute must for astrology lovers. It is an attractive, visual application that will help you learn more about planets and stars.