Stellarium
Is another can’t live without.
What it does is
Stellarium renders 3D photo-realistic skies in real-time. With stellarium, you really see what you can see with your eyes, binoculars or a small telescope.

Some features:

– Over 120000 stars from the Hipparcos Catalogue with name and infos for the
brightest ones,
– Planets in real time, with a powerful zoom mode to see them like in a
telescope,
– Drawing of the 88 constellations with their names,
– Drawing of more than 40 messiers objects (Orion, M31 etc..),
– Photorealistic Milky Way,
– Ground, fog, and landscape,
– Clickable stars, planets and nebulas with informations,
– Windowed and fullscreen modes.