Stellarium is a free, Open Source planetarium for your computer that shows a realistic sky in stunning 3D. Also available as a Portable version.

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 spherical panorama projection

Customizability:
● Add your deep-sky objects, landscapes, constellation images, and scripts