Sunspots & the Solar Cycle

Cool, dark, and driven by magnetism

A sunspot is a patch of the Sun's visible surface where the magnetic field is so concentrated that it chokes off the rising flow of hot gas from below. Starved of that heat, the spot cools to around 3,800 °C — still ferociously hot, but cooler than the roughly 5,500 °C surface around it, so it looks dark by contrast. Sunspots come in groups, can dwarf the Earth, and drift across the disk as the Sun rotates, lasting from days to months.

Sunspots are the visible tally of the Sun's magnetic activity, and that activity runs on the solar cycle. Discovered in the 1840s, the cycle sees sunspot numbers climb to a busy solar maximum and fall to a quiet solar minimum about every 11 years. At each maximum the Sun's entire magnetic field flips north-for-south, so the true magnetic period is about 22 years. Around maximum, the twisted magnetic fields of active regions snap and reconnect, unleashing solar flares and coronal mass ejections (CMEs) — billion-ton clouds of charged particles flung into space. When those clouds sweep past Earth they drive space weather: gorgeous auroras, but also risks to satellites, GPS, radio, and power grids.

Watch the Sun turn, one spot at a time

Sunspots are the most rewarding everyday solar-observing target — but the same iron rule applies: never look at the Sun without proper protection. With a certified white-light solar filter over the front of a small telescope, or by the projection method, large sunspot groups are easy to see as dark blotches, often with a darker core (umbra) ringed by a greyer border (penumbra). Big groups are even visible through ISO 12312-2 eclipse glasses with the naked eye.

The real fun is tracking them over time. Because the Sun rotates about once a month, a sunspot group visibly marches across the disk over roughly two weeks — sketch or photograph it every clear day and you'll watch the Sun spin. During periods of high activity, keep an eye on space-weather alerts: a strong geomagnetic storm can push the aurora to surprisingly low latitudes, and that is a naked-eye spectacle worth chasing to a dark northern horizon.

Not holes, not a steady star

The most common misconception is that sunspots are holes in the Sun. They are not — the Sun has no solid surface to have holes in. A sunspot is simply a cooler, magnetically throttled patch of the same glowing plasma, dark only in comparison to its blazing surroundings. The second misconception is that the Sun is a constant, unchanging star. It isn't: its output and appearance vary continuously with the cycle. History even records a stretch from about 1645 to 1715, the Maunder Minimum, when sunspots nearly vanished for decades — a quiet Sun that coincided with an especially cold spell in Europe often called the Little Ice Age.

The aurora that sunspot storms create carries its own deep well of legend. Norse tradition tied the lights to the Valkyries; the Sámi and many northern peoples read meaning into them; and for centuries a red aurora was taken as an omen of war or blood. The science is grander than the omen: you are watching particles from the Sun, flung out by a magnetic storm, lighting up the top of our own atmosphere.

Step into the myths written across the night sky →