Stellarium is a free open-source planetarium for your computer that shows a realistic sky in stunning 3D. 32-Bit available.

You see what you would see with the naked eye, binoculars or a telescope which allows it to be used in planetarium projectors. Just set your coordinates and blast off to the stars.

Stellarium Features:

Sky:
default catalog of over 600,000 stars
extra catalogs with more than 210 million stars
asterisms and illustrations of the constellations
images of nebulae (full Messier catalog)
realistic Milky Way
very realistic atmosphere, sunrise and sunset
the planets and their satellites

Interface:
a powerful zoom
time control
multilingual interface
scripting to record and play your own shows
fisheye projection for planetarium domes
spheric mirror projection for your own dome
graphical interface and extensive keyboard control
telescope control

Visualization:
equatorial and azimuthal grids
star twinkling
shooting stars
eclipse simulation
skinnable landscapes, now with spheric panorama projection

Customizability:
add your own deep sky objects, landscapes, constellation images, scripts...