SCIENCE · WHAT IF · PART 1 OF 3

What If the Sun Went Out?

October 2026

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Eight minutes of borrowed light

Sunlight is not instant. It crosses roughly 149.6 million kilometres at the speed of light, and the trip takes eight minutes and twenty seconds. Every ray of sunshine you have ever seen was already in the past when it reached you. So if the sun went dark, the last light already in transit would keep the morning looking perfectly ordinary for just over eight minutes. People would finish conversations, pour coffee, glance at a normal blue sky. Then the supply would run out — all at once, everywhere.

Not night-black. Space-black.

The darkness that followed would not resemble nightfall. The blue of the daytime sky is sunlight scattered by the air itself; with no sunlight to scatter, the blue goes too. What remains is the black of space, with stars visible at noon. The Moon would vanish from view as well — it has no light of its own and only ever shone with borrowed sunlight. The planets would fade for the same reason. In a single moment, the sky would stop being a ceiling and become a window.

Day one: every leaf stops working

The first casualty would not be warmth. It would be photosynthesis. The moment the light ends, the process that feeds nearly all life on Earth doesn't slow down — it halts. Planetary scientists who have modelled this scenario for Popular Science note that most plants would die within a few weeks without it, living briefly on stored reserves. The entire food web, from grass to grain to everything that eats either, runs on that one reaction. On day one of the dark, the engine at the bottom of the world switches off.

The cold is the real killer — and it doesn't wait

Earth is warm because it banks heat from the sun faster than it leaks heat to space. Cut the income and the planet simply radiates its savings away, with nothing coming back in. According to estimates by MIT atmospheric scientist Timothy Cronin, the average surface temperature would fall below the freezing point of water in about a week. Caltech planetary scientist David Stevenson offers a stronger-end estimate for the same week: an average below 0°F. These are estimates, not measurements — but they agree on the shape of the curve. Lakes would skin over with ice, and the poles would stop being special. Everywhere would be becoming the pole. And that is only week one. Part 2 is the freeze.

The takeaway

• If the sun went dark, Earth would get eight minutes and twenty seconds of normal-looking morning — the last sunlight already in transit — before the sky went black.
• The blackout would be total: no scattered blue sky, stars at noon, and the Moon and planets gone, since they shine only by reflected sunlight.
• Photosynthesis halts the instant the light does; most plants would die within weeks, cutting the food web off at its base.
• Expert estimates put the global average temperature below freezing within about a week — one stronger-end estimate says below 0°F.
• The light dies in eight minutes. The warmth leaves far more slowly. That gap is the whole story.

So tell us — day one of the dark: what's the first thing you do?

The story continues: Part 2 — The Year Earth Froze and Part 3 — What Survives a Year Without the Sun? The cold was only the beginning — next, the oceans seal shut, and the ice does something nobody expects.