We know space is big, but trying to understand how big is tricky. Say you stare up at the sky and identify stars and constellations in a virtual planetarium, you can't quite fathom how far away all those stars are (previously, twice). Even if you could change your point of view and zoom around in space to really see 100,000 nearby stars (autoplaying ambient music, and there are actually 119,617 stars mapped in 3D space), it's still difficult to get a sense of scale. There's this static image of various items mapped on a log scale from XKCD (previously), and an interactive horizontal journey down from the sun to the heliosphere with OMG Space (previously). You can get a bit more dynamic with this interactive Scale of the Universe webpage (also available in with some variants, if you want the sequel [ previously, twice], the swirly, gravity-optional version that takes some time to load, and the wrong version [previously]), but that's just for the scale of objects, not of space itself. If you want to get spaced out, imagine if If the Moon Were Only 1 Pixel, and travel from there (previously). This past March, BBC Future put out a really big infographic, which also takes a moment to load, but then you can see all sorts of things, from the surface of Earth out to the edge of our solar system.
In the seventeenth and eighteenth centuries it became possible to believe in the existence of life on other planets on scientific grounds. Once the Earth was no longer the center of the universe according to Copernicus, once Galileo had aimed his telescope at the Moon and found it a rough globe with mountains and seas, the assumption of life on other planets became much less far-fetched. In general there were no actual differences between Earth and Venus, since both planets orbited the Sun, were of similar size, and possessed mountains and an atmosphere. If there is life on Earth, one may ponder why it could not also exist on Venus. In the extraterrestrial life debate of the seventeenth and eighteenth centuries, the Moon, our closest celestial body, was the prime candidate for life on other worlds, although a number of scientists and scholars also speculated about life on Venus and on other planets, both within our solar system and beyond its frontiers. Venusians: the Planet Venus in the 18th-Century Extraterrestrial Life Debate (PDF), from The Journal of Astronomical Data (JAD) Volume 19, somewhat via NPR and their mention of amateur astronomer Thomas Dick's estimations of the populations of the other planets in our solar system (Archive.org online view of Celestial scenery, or, The Wonders of the planetary system displayed, 1845).
If the Moon Were Only 1 Pixel is a tediously accurate model of the Solar System that Josh Worth made to explain to his daughter just how difficult it is to go on holiday to Mars.
I am a staunch believer in leading with the bad news, so let me get straight to the point. Earth, our anchor and our solitary haven in a hostile universe, is in a precarious situation. The solar system around us is rife with instability.[more inside]
The cosmos is also within us, we're made of star-stuff. We are a way for the cosmos, to know itself.
Cosmos: A Personal Voyage is a thirteen-part television series of one hour shows written by Carl Sagan, Ann Druyan, and Steven Soter, that was aired at the tail end of 1980 and was - at the time - the most widely watched series in the history of American public television. It is best introduced by an audio excerpt of one of his books, The Pale Blue Dot. Inside is a complete annotated collection of the series. [more inside]
What lives where in the Solar System. Fantastic Adventure covers from 1939/40 depicting the kind of lifeforms they think each planet can support. [more inside]
Take a tour of the solar system! Tonight, see the wonders of Mercury, Venus, Jupiter, Mars and Saturn! There's only one catch: You'll need to actually step outside to do it. [more inside]
At forty miles (64.4 km) from Pluto to Sun, the Maine Solar System Model is the largest complete three-dimensional scale model of the solar system in the world. What, you didn't know there was more than one? And yes, Pluto is staying put.