Sun Activity
The Sun's changing activity — sunspots, flares, and the solar cycle.
Overview
The Sun's magnetic activity rises and falls over a cycle averaging about eleven years, tracked most visibly through sunspot numbers. The cycle drives flares, coronal mass ejections and the general level of space weather, and its detailed behaviour is still not predictable in advance.
- Sunspots are cool, dark regions where strong magnetic fields suppress convection.
- The full magnetic cycle is about 22 years; the sunspot cycle of 11 years is half of it.
- Cycle strength varies substantially and is not reliably predictable.
- The Maunder Minimum shows the cycle can nearly stop for decades.
What sunspots are
Sunspots are regions where magnetic field lines emerging through the photosphere are strong enough to inhibit convection, so less heat reaches the surface there. They are around 1,500 kelvin cooler than the surrounding photosphere, which makes them look dark by contrast — in isolation a sunspot would still be brighter than most artificial light sources.
They typically appear in pairs or groups of opposite magnetic polarity, marking where a loop of field has broken through. Individual spots last from days to weeks, and their positions and motions are how the Sun's differential rotation was first measured: the equator rotates faster than the poles.
The cycle
Sunspot numbers rise and fall with a period averaging about eleven years, though individual cycles range roughly from nine to fourteen. At solar minimum the disc can be blank for extended periods; at maximum, dozens of spots may be present with frequent flares and coronal mass ejections.
The magnetic reality is a 22-year cycle. The Sun's global magnetic polarity reverses at each sunspot maximum, so it takes two sunspot cycles to return to the original magnetic configuration. Spot groups also migrate from mid-latitudes toward the equator as a cycle progresses, producing the butterfly diagram — one of the longest-running datasets in observational astronomy.
Why the cycle is not predictable
The cycle originates in a magnetic dynamo driven by convection and differential rotation in the Sun's interior, and while the broad mechanism is understood, forecasting the amplitude of the next cycle remains unreliable. Predictions for recent cycles have spanned a wide range, and outcomes have repeatedly fallen outside the consensus expectation.
The historical record shows the variability is real and can be extreme. During the Maunder Minimum, roughly 1645 to 1715, sunspots nearly vanished for decades — an episode documented by contemporary observers and independently corroborated by cosmogenic isotope records in tree rings and ice cores.
Observing the Sun safely
The Sun is the one object that can cause permanent injury in the time it takes to look at it, and through an unfiltered telescope the damage is instantaneous. Any solar observation requires a purpose-made filter mounted on the front of the instrument, never at the eyepiece where concentrated heat will crack it.
Projection is a completely safe alternative: a small telescope or binoculars projecting the solar image onto white card shows sunspots clearly, and it is how the historical sunspot record was largely compiled. Specialist hydrogen-alpha telescopes reveal prominences and filaments in the chromosphere that white-light observation cannot show at all.
Continue in the data
Catalogues, hubs, and reference pages that hold the underlying records for this topic.
Frequently asked
- What are sunspots?
- Regions of the photosphere where strong magnetic fields suppress convection, so less heat reaches the surface. They are around 1,500 kelvin cooler than their surroundings and appear dark only by contrast — a sunspot removed from the Sun would still glow brilliantly. They usually appear in groups of opposite magnetic polarity.
- How long is the solar cycle?
- The sunspot cycle averages about eleven years, with individual cycles ranging roughly from nine to fourteen. The underlying magnetic cycle is about 22 years, because the Sun's global magnetic polarity reverses at each sunspot maximum and takes two sunspot cycles to return to its original configuration.
- Can the next solar cycle's strength be predicted?
- Not reliably. The cycle arises from a magnetic dynamo in the Sun's interior whose behaviour is understood in outline but not in enough detail to forecast amplitude. Predictions for recent cycles have varied widely and outcomes have repeatedly fallen outside the expected range.
- How can I observe the Sun safely?
- Only with a purpose-made solar filter mounted on the front of the instrument, or by projecting the image onto white card. Never look through an unfiltered telescope or binoculars — the concentrated light causes severe injury almost instantly, and eyepiece-mounted filters can crack under the heat. Projection is entirely safe and shows sunspots well.