The Overview Effect is a term describing the cognitive effects of viewing Earth from space. The best-known example hit us just over forty years ago, when the famous Blue Marble photograph was taken, and the world realized: we are all living together on a tiny island in the vastness of space (to paraphrase Carl Sagan).
The change from Earth-dweller to space-farer was profound, and it is hard for me to understand that effect, because I've grown up with the Blue Marble as a common image. I imagine it's a little like explaining to a teenager today what a mix tape was, and why it mattered -- the kid will intellectually understand what a mix tape was ("it's like a playlist!"), but may never emotionally understand the power of the song selection process, the work it took to create, and the sheer emotion of this little object situated in time. Now take "mix tape" and sub in "the entire world" and perhaps the scale of emotion may be clearer.
In the 20-minute documentary OVERVIEW (embedded below), five astronauts and various philosophers explain their experiences with the Overview Effect, and why it matters. This is a must-see for space enthusiasts.