Why do sunspots look black?
The short answer
Sunspots are not dark. They are patches of the Sun's surface that are cooler than their surroundings, roughly 3,500C against about 5,500C. That contrast makes them look black. Cut one out and hang it alone in the night sky and it would glow brighter than a full moon.
The darkness is pure contrast
A sunspot is still blisteringly hot, around 3,500C, which is hotter than anything you will ever encounter on Earth outside a laboratory. It only looks black because it sits next to a surface roughly two thousand degrees hotter and correspondingly brighter. Your eyes and cameras adjust to the bright surroundings, and the cooler patch falls into shadow by comparison. Isolate it and it would be dazzling.
Knots in a magnetic field make the spots
The Sun is an enormous magnet with field lines looping from pole to pole. It is also not solid, so it does not rotate as one piece: the equator spins faster than the poles. Over time that differential rotation stretches, winds and tangles the field lines. When a tangled bundle becomes knotted enough, it bursts up through the surface like a loop of rope breaking the surface of water. Where the loop punches through, it blocks the hot gas rising from below, that patch cools, and a sunspot appears.
They arrive and fade on an eleven-year rhythm
Sunspot numbers are not random. Some years the Sun's face is nearly blank; then spots multiply, peak, and dwindle again. The full cycle takes roughly eleven years and then repeats. People have been counting sunspots systematically since the 1600s, which makes it one of the longest continuously running scientific records in existence. Individual cycles vary in strength, so eleven years is an average rather than a timetable.
Twist a magnetic field far enough and it snaps
Keep twisting a rubber band and eventually it fails. The Sun's tangled field lines do something similar. When they snap and rearrange, they release a colossal burst of energy called a solar flare. These are the largest explosions in the solar system by a wide margin. Sometimes the Sun follows a flare by hurling billions of tonnes of its own material into space, an event called a coronal mass ejection.
Earth has a shield, and it turns storms into light
Earth is itself a magnet, wrapped in a magnetic field that deflects most of the incoming solar material smoothly around the planet, the way a river parts around a stone. It has done this for billions of years. Some particles do get in near the poles, following field lines down into the upper atmosphere, where they make the air glow. That is the aurora. The most violent weather in the solar system arrives at Earth as the most beautiful thing in the sky.
It is not entirely harmless
Strong solar storms can disrupt satellites, interfere with GPS accuracy and, in extreme cases, affect power grids. This is why space weather forecasting exists as a real discipline, with agencies watching the Sun daily and issuing predictions much like a weather service. The forecast is not rain or sunshine but sunspot counts, flare probability and aurora likelihood.
Sources
Full transcript: Why the Sun Has Black Spots?
Sunspots and solar flares. By now, you know the Sun pretty well. A giant ball of glowing gas, steady as anything, shining exactly the same every single day. Right?
Look closer. Are those freckles? [snorts] The Sun has spots, and where there are spots, there are storms. The Sun has weather.
Welcome back to What and Why. Today, sunspots, solar flares, and the wildest weather in the solar system. Plus, the beautiful gift it sends us. Let's zoom right in on a sunspot.
It looks black, but it's not actually dark. A sunspot is just a patch that's cooler than the blazing surface around it. And cooler here still means about 3 and 1/2 thousand degrees. If you could cut a sunspot out and hang it in the night sky, it would glow brighter than the full moon.
It only looks dark next to its neighborhood. So, why do cool patches happen? Because the Sun is a giant magnet with invisible field lines looping from pole to pole. Now, here's the strange part.
The Sun doesn't spin like a solid ball. The middle spins faster than the top and bottom. So, those tidy field lines get stretched and wound and twisted into a tangled mess. And when a twisted bundle of field lines gets knotted enough, it poaks right up through the surface, like a loop of rope bursting out of the water.
Where the loop punches through, it blocks the hot gas bubbling up from below. The surface there cools down, and hello, a pair of sunspots. Knots make spots. Here's something lovely.
The spots keep a schedule. Some years, the Sun is nearly blank. Then, more and more spots appear, then they fade away again. The whole rhythm takes about 11 years, and then it repeats.
People have been counting sunspots since the 1600s, one of the longest science projects in history. Now, what happens to a knot that keeps twisting tighter and tighter? Think of a rubber band. Twist, twist, twist, snap.
When the sun's tangled field lines snap, they release a colossal flash of energy, a solar flare. One flare can carry more energy than millions of volcanoes, the biggest explosions in the solar system, and they're happening on our own star. Sometimes, after a big snap, the sun does one better. It hurls a whole glowing blob of itself into space.
Billions of tons of particles flying off like a giant solar sneeze. Grown-ups call it a coronal mass ejection. We'll stick with sneeze. And sometimes, that sneeze heads our way.
Should we worry? Nope, and here's why. Earth has an invisible shield. Our planet is a magnet, too, wrapped in its own field lines.
When the solar sneeze arrives, the shield bends it smoothly around us, like a river flowing around a stone. It has protected Earth for billions of years. Storms slide right past. But a little of that solar stuff sneaks in at the poles, sliding down the field lines like a slide.
And when it touches the top of our air, the sky begins to glow. Curtains of light rippling in the dark, the northern and southern lights, auroras. The sun's wildest weather arriving as the gentlest, most beautiful show on Earth. Solar storms can make satellites hiccup and GPS wobble.
So, scientists watch the sun every day and make a forecast. Not rain or snow, but space weather. Good morning. Two sunspots, medium chance of flares, aurora likely up north.
What would like that job? Remember, sunspots are cooler magnetic freckles. Solar flares are magnetic knots snapping, the biggest explosions in the solar system. And Earth's shield turns those storms into auroras.
Next time, the grand finale. The whole life of our sun, where it came from, and the long, bright future ahead. See you on What and Why.
Transcript of the episode, lightly cleaned for readability.
Sample question
Question 1 of 10
Why do sunspots appear dark?
- They are cooler than the surrounding surface, so they look dark by contrast correct
- They are holes straight through the Sun
- They are shadows cast by planets
- They are clouds of dust
A sunspot is around 3,500C against a background of about 5,500C. The contrast is what makes it look black.
That is one of 10. The rest are not shown here, and the answer order changes every time you take the quiz.
Written by Watt & Why. Published 14 October 2026. Last reviewed 17 October 2026.