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.
Features:
Sky
default catalogue of over 600,000 stars
extra catalogues with more than 210 million stars
asterisms and illustrations of the constellations
constellations for 20+ different cultures
images of nebulae (full Messier catalogue)
realistic Milky Way
very realistic atmosphere, sunrise and sunset
the planets and their satellites
Interface
a powerful zoom
time control
multilingual interface
fisheye projection for planetarium domes
spheric mirror projection for your own low-cost dome
all new graphical interface and extensive keyboard control
telescope control
Visualisation
equatorial and azimuthal grids
star twinkling
shooting stars
eclipse simulation
supernovae simulation
skinnable landscapes, now with spheric panorama projection
Customizability
plugin system adding artifical satellites, ocular simulation, telescope configuration and more
ability to add new solar system objects from online resources...
add your own deep sky objects, landscapes, constellation images, scripts...