The Sun is a complex and wonderful star that is stable enough for life to exist on Earth as it is a dependable source of light and heat, never faltering. The power of the Sun can be felt in the heat it supplies here 93 million miles away that can cause painful sunburn if we are not careful. As respected as the Sun is, it can throw temper tantrums. One of them was so bad that it disrupted civilization for days; today it would be apocalyptic with the technology we depend on. A warning of an impending temper tantrum can be credited to the most obvious feature, the sunspot.

Sunspots can be larger than Earth, which means they can be seen with the unaided eye when the Sun is low on the horizon shining through a thick layer of haze. A history of sunspot sightings is found in ancient Chinese records, but it was the invention of the telescope in 1610 that allowed Galileo to study them. Individual sunspots last only a few weeks but the rate of appearances and disappearances is cyclical. This is known as the sunspot cycle where the number of sunspots increases and decreases every 11 years. The cycle is not exact, but comes close, and each peak in the sunspot cycle is different than the preceding ones.

Sunspots appear dark because they are cool relative to the rest of the Sun. They are about 7000ºF compared to 10,000ºF for the Sun’s surface. If a sunspot could be placed by itself in the night sky it would appear like a reddish star, 10 times brighter than the full Moon. The relative darkness and coolness are due to the intense magnetic fields that generate them. The magnetic fields prevent convection that normally transports energy towards the surface. Sunspots form in pairs with each leading spot having the same polarity as all the other pairs in that hemisphere. The polarity remains the same throughout the 11-year cycle, but when a new 11-year cycle begins, the polarity of the sunspots in the pair is reversed. After this cycle ends, the polarity is back to that of the initial cycle. So, the sunspot cycle is actually part of a 22-year magnetic cycle. How and why the polarity switches is one of the Sun’s greatest mysteries.

Sunspots are a source of solar flares, the most violent explosions in the Solar System. Sunspots are strongly magnetic and if these fields become twisted too much, they will kink and reduce their twist abruptly. This sudden release of energy results in flares, which can pack a punch of more than a billion one-megaton thermonuclear explosions. A flare with this much power can propel high-energy particles up to one-third the speed of light. When these particles interact with Earth’s magnetic field, or any other planet’s, they can create aurora, interrupt radio communications, induce currents in electrical power grids large enough to blow out transformers, and confuse birds’ navigation. Solar flares have crippled and destroyed satellites and spacecraft, and pose a radiation danger to astronauts, especially on long journeys to Mars, since they cannot readily be predicted.

The Earth’s climate may be affected by sunspots in ways that are not yet fully understood. There was a period from 1640 to 1710 where the cycle ceased and there were hardly any sunspots. This period is known as the Maunder Minimum and coincided closely with a period of intense, cold weather in northern Europe known as the “Little Ice Age”. It was so cold that rivers that never froze were suddenly frozen solid enough for skating and oxen could haul lumber across them. The summers were so chilly that there was frost every month including July. Any crops that managed to grow did not live long enough to reach harvest before an early freeze killed everything. Famine and disease were widespread and many plagues broke out resulting in unprecedented loss of life. Spacecraft have proven that the Sun’s energy output increases as the sunspots increase and therefore may have a direct relationship to Earth’s climate.

The Sun proved its power in September 1859 just before the solar sunspot maximum of 1860 when a huge cluster of sunspots grew rapidly during August 1859 to the amazement of many. Richard Carrington was an amateur skywatcher near London where he sketched sunspots safely, but on September 1 he was blinded by a sudden flash of light. This was a white light flare that lasted about five minutes. The flare was accompanied by a coronal mass ejection, a burst of magnetized plasma from the Sun’s upper atmosphere. They usually reach Earth in a few days, but this one was so powerful that it took only 17.6 hours. It triggered a huge geomagnetic storm that wreaked havoc with technology. The Earth fell silent as telegraph communications around the world failed. Sparks showered from telegraph machines triggering fires and telegraph operators received electric shocks. Auroras were seen in the tropics including Cuba and Hawaii. They were so bright that it seemed like a false dawn with birds chirping at night. It was impossible to transmit and receive telegraph messages for days, and yet operators could unplug their equipment and transmit messages using only the auroral current. This powerful display of the Sun in 1859 is known as the Carrington Event.

These storms rarely pose a direct threat to human life but can impact safety-critical systems with its electromagnetic effects such as space-based communications, navigation, weather forecasting services and electrical power distribution. Another Carrington Event in this modern era of computers would cause an internet apocalypse, sending large numbers of people and businesses offline. It is considered one of the most serious natural hazards and could cause up to three trillion dollars in damages to the U.S. alone. A powerful geomagnetic storm occurred during March 1989 that knocked out Quebec’s power grid and produced a spectacular display of auroras that were seen as far south as Florida. Locally, the auroral display was one of the most memorable due to its brightness; it rippled and pulsated all the night of March 12, thankfully without power interruption.

It is not known when another Carrington Event might occur. It is often considered a once in 500 years event but can strike again without ample warning. Storms half as strong do occur more often and companies have contingency plans to deal with them. The Sun is like a dragon – unpredictable and dangerous. When it unleashes its fiery breath, we are usually treated with beautiful auroras, but when truly angry, we must beware of a crippling geomagnetic storm. This dragon can never be slayed or tamed. It must be treated with respect.