Sunspots and Auroras — How Solar Activity Affects Earth
From dark blemishes on the Sun's surface to auroras painting the night sky — here's how solar activity, rising and falling on an 11-year cycle, affects Earth and our daily lives.
Dark spots on the Sun's surface — sunspots
Observe the Sun safely with a proper solar filter, and you'll spot dark patches on its surface. These "sunspots" aren't actually dark — they're simply somewhat cooler (about 4,000°C) than the surrounding surface (about 5,500°C). Bundles of strong magnetic field suppress the convection of hot gas in these regions, so they appear comparatively dim.
A single sunspot can range from Earth-sized to larger than several Earths combined. Because sunspots mark concentrations of strong magnetic field, they're also the simplest gauge of how active the Sun's magnetic activity currently is.
An 11-year rhythm of solar activity
Heinrich Schwabe, a 19th-century German pharmacist and amateur astronomer, tracked sunspots for decades and discovered that their numbers weren't constant — they rose and fell on a roughly 11-year cycle. The period with the most sunspots is called "solar maximum"; the period with the fewest, "solar minimum."
This 11-year cycle is understood to be tied to the Sun's complex internal magnetic field twisting and reorganizing itself. During solar maximum, not just sunspots but also explosive events on the Sun's surface — flares and coronal mass ejections (CMEs) — become more frequent.
From the Sun to Earth — solar wind and auroras
Even during quieter periods with few sunspots, the Sun continuously streams charged particles into space — the "solar wind." When the Sun erupts with a CME, far more particles than usual head toward Earth. Fortunately, Earth's own magnetic field (the magnetosphere) deflects most of them, but some funnel down along magnetic field lines near the poles.
When these particles strike oxygen and nitrogen atoms high in the atmosphere, they transfer energy, and those atoms release it again as light, painting the night sky — this is the "aurora." Oxygen atoms mostly produce green and red light; nitrogen atoms, blue and purple.
How solar storms affect civilization
Powerful solar storms don't just produce beautiful auroras — they cause real damage too. During the 1859 "Carrington Event," the strongest solar storm on record, surges of current in the era's newly built telegraph lines reportedly caused sparks and even fires. In a society as dependent on satellites, power grids, and GPS as ours, a storm of similar magnitude today would cause far greater disruption.
That's why space weather observatories around the world monitor solar activity in real time, issuing advance warnings to satellite operators, airlines, and power companies whenever a strong flare or CME is detected. During periods of high solar activity, auroras also become visible at lower latitudes than usual — worth keeping an eye on the night sky news around solar maximum.