Free Software to Explore Stars and Galaxies: Celestia || Free Software

Here are some of the features of Celestia as available in its documentation:

Hover over each of the planets in our Solar System as they rotate slowly below you. See clouds drift by (where applicable) and shadows being cast on mountains and craters as the Sun sets low.
Fly along with Mariner 10 on its historic flyby of Mercury.
Visit the searing surface of Venus and view it in a panoramic 360° vista from the surface.
Take a spin down to the Earth’s surface in your own hyperdrive spacecraft. Skim over the oceans of Earth as you fly below the clouds. Soar back into space to see the lights come on in the cities of Earth.
Be present as Apollo 11 lands on the Moon in 1969, or fly by Sputnik 1 in 1958 shortly after its launch.
Rendezvous with the ISS or the Hubble Space Telescope. Attempt a docking at the ISS Shuttle port.
Jump at hyperspeed to the Andromeda spiral galaxy, M 87 located in the rich Virgo Cluster or the beautiful Whirlpool galaxy, or visit over ten thousand galaxies, accurately drawn.
Learn what efforts are being taken to discover if extraterrestrial intelligence exists in the universe.
Peer through the primary focus from inside the Hale Telescope on Palomar mountain.
View Earth’s Magnetic Field from space and see the Aurora glowing and shimmering.
See the massive size of Hurricane Katrina as it makes landfall on New Orleans.
Hover over Mar’s Gusev crater and Meridiani Planum and drop down to visit Spirit and Opportunity, then fly over to Olympus Mons and Valles Marineris and fly through the canyon itself.
Be there in the year 2029 when the asteroid Apophis will approach Earth on a possible collision course.
Observe a spectacular lunar eclipse of our own Moon and a total solar eclipse on Earth.
Display an internal X-section of Earth and peer deeply into its tectonic layers and structure.
Discover Mir as it passes over the Russian homeland with its cosmonaut crew onboard.
Position yourself above Jupiter and watch as its large moons drift across the face of the planet, casting multiple eclipse shadows on its banded clouds and Great Red Spot.
Examine the actively erupting volcanoes on Jupiter’s moon Io. Fly through a spewing volcanic plume.
Hover far beyond Saturn, plunge through its rings, and count its 60 moons.
Witness Cassini arrive in Saturn space in 2004 and drop the Huygens probe into the atmosphere of Titan in January 2005. Follow Huygens down toward a parachute landing on Titan’s surface.
Seek out Ceres, Eris and Makemake, our Solar System’s newest “dwarf planets”.
Fly out to the edges of our Solar System and follow Voyagers 1 and 2 as they head to distant stars.
Witness the impact of the Deep Impact spacecraft onto the surface of comet Tempel1 in July 2005.
Travel to the heart of Betelgeuse, a distant Red Supergiant star that will Hypernova someday.
See stellar creation from deep within the Rosette and Eagle Nebulas, giant stellar nurseries.
Set your ship at faster-than-light speed and sail to Rigel Kentaurus A, located 4.3 light years away.
View the red glow of sunlight on Gliese 581c, an earthlike world orbiting it’s small red dwarf star.
Travel in time to 3000 CE to witness giant mirrors melt the Martian polar ice caps and help to terraform Mars into a verdant world of water, plants and cities of the future.
Cruise next to Cosmos, a revolutionary new spacecraft that may someday “sail” on a wind of pure sunlight.
Travel backward in time 4 billion years to witness the planet “Orpheus” catastrophically collide with Earth to actually form our Moon.
Travel far into the future and rendezvous with a colossal rotating Space Station as it orbits Earth.
Journey to the edges of a massive rotating Black Hole as it spins near its stellar companion. Witness another Black Hole swallowing its companion star.
Journey to the frozen wasteland of Pluto and its three moons and see their icy coldness for yourself.
Take up station behind comet Halley in 1986 as its gaseous lavender tail streams out behind it near Earth.
Observe for yourself the deep field galaxies that were photographed by the Hubble Space Telescope.
Hear the pulses of the new pulsar in the Crab Nebula, spinning before you at over 30 times a second.
Witness the end of Earth, as it is swallowed by our swelling Red Giant sun billions of years from now.
Fly directly through a theoretical wormhole on your way to a distant solar system.
Explore numerous fictional solar systems, complete with meticulously detailed, exotic alien civilizations, terraformed moons, futuristic space stations, space fleets, and interstellar spacecraft.
Travel in tandem with the USS Enterprise commanded by Captain Picard as it battles the Borg Empire.
Travel in the whimsical world of Hollywood and visit the StarWars® worlds of Tatooine, Endor and Hoth. Fly next to the Imperial Death Star or Star Destroyer as the Millennium Falcon swoops in for an attack.