The glowing edge of space, or how the expansion of the universe is affecting the visible spectrum.
We’ve already seen how mankind conquered the night, but why is the sky dark after nightfall in the first place? The real reason, like most of science, is far less obvious than it seems, and far more expansive. Count on the fine folks of MinutePhysics — who have previously explained why the color pink doesn’t exist and why the past is different from the future — and their signature hand-drawn animation to illuminate the answer. And if Richard Feynman didn’t give you enough pause in demonstrating that the fire in your fireplace is actually the light and heat of the sun, how about knowing that the glow of the sky you see today isn’t starlight but leftover light from the Big Bang? Now that’s a moment of cosmic awe.
All of our evidence seems to indicate that space has no edge, but the universe itself does — not a spatial edge, but a temporal one.
For a less scientific but no less delightful take on the subject, see Edward Gorey’s characteristically irreverent and altogether fantastic Why We Have Day and Night.