When I was a kid, I read The Magician's Nephew by CS Lewis. In chapter 4, Polly and Digory magically transport themselves to a world bathed in red light - as though from a dying sun. All the buildings were ancient, crumbling, and ruined.
Some years later at University, I was studying a sci-fi/fantasy/speculative fiction subject for my degree. I was struck once more by a visual similar to the red-lit world in The Magician's Nephew.
In HG Wells' The Time Machine, the time-travelling protagonist flings himself far far into the human future and saw not only that evolution had continued and made short work of humanity's existence, but that the sun had expanded greatly in its old age and was bathing everything in ember light.
These literary experiences helped to frame one of my reference points in life - that we are one species on one tiny planet in a vast universe that's ever-changing. Time marches on no matter what we do or what we believe. And one day, even the sun will engulf our earth, become a gigantic glowing ember, and eventually a black stellar corpse.
Perhaps it's a grim thought, but I like to think that it can help provide human life with some meaning too. Our lives may be short, but as Seneca suggests, a human life can be meaningful if we don't waste it.