We live at the whim of a “stormy star.” While our Sun sustains life on this planet, it is also prone to explosive acts of energy and violence. Once every 11 years, our Sun reaches a maximum level of activity and releases great outbursts of energy known as solar flares and coronal mass ejections (CMEs). These discharges are the equivalent of billions of megatons worth of TNT, with the energetic fast gamma- and X-ray energies hitting Earth in minutes and the heavier particles impacting our magnetic field days later. Luckily, not all of these outbursts are directed toward Earth, and we have a fleet of observatories in space and on the ground monitoring our Sun for these potential hazards. Most solar storms go unnoticed, but some wreak havoc with communications, satellites and pose a radiation hazard to astronauts in space. And as our society becomes ever more dependent on technology, the chances increase that a large solar storm could seriously impact civilization. Following are some of the biggest solar storms witnessed over the last two centuries.
10. New York Railroad Storm
On May 13, 1921, astronomers observed a huge 94,000-mile-wide sunspot on the center of the solar disk. Auroras were seen on following evenings across Europe and as far south as California. On the morning of May 15, a good portion of the New York Central Railroad was put out of action as a result of current induced by the storm. Some of the control offices for the railroad even experienced a ground current overload that set them aflame. Much of the Eastern Seaboard experienced a communications blackout in one of the largest solar storms of the early 20th century.
9. July 2012 Solar Flares
On July 12, 2012, sunspot active region 1520 unleashed a large X1.4-class flare Earthward. The flare triggered aurorae and numerous radio blackouts. X-class flares are the most powerful type of solar flare; the higher the subsequent number, the more powerful the flare. The same region of the Sun released a more powerful X5.4 flare earlier in the month, although the X1.4 was more significant in its impact to the local space environment. Most flares do not impact the Earth, and the significance of an event is determined not only by how strong a flare is, but how it affects our magnetic field.
8. Apollo 16 and the 1972 Solar Flare
Space travel during solar maximum, when the Sun is at its most active, can be a risky proposition. Early Apollo flights enjoyed a solar minimum, but as Solar Cycle 20 progressed, each flight to the Moon risked exposure. Apollo 16 just missed an X2-class flare in August 1972 that would have posed a major problem if astronauts had been on the Moon at the time. It has been estimated that an exposed astronaut would have received 300 rems of radiation, an amount that would have had about a 50 percent chance of being fatal within 60 days.
7. 2000 Bastille Day Solar Flare
On July 14, 2000, solar observation satellites recorded a powerful X5.7-class flare on the surface of the Sun. Energetic protons swamped detectors, and the event was seen as far away as the Voyager I and II spacecraft on the edge of the solar system. The event triggered widespread radio blackouts, and was energetic enough that air travelers along polar routes received the equivalent of several chest X-rays worth of radiation exposure.
6. August 2011 Solar Flare
The sputtering start of the current solar cycle No. 24 finally got underway in earnest on Aug. 9, 2011, when the Sun unleashed an X6.9 flare. This was one of the largest thus far for cycle No. 24. NASA’s newest solar observing satellite, the Solar Dynamics Observatory, observed the event, and the flare also briefly ionized the upper atmosphere of the Earth, causing radio disruptions.
5. December 2006 Solar Flare
Luckily, the Earth is a small target for space weather activity. On Dec. 5, 2006 a flare registering X9 erupted on the limb of the Sun. One of the largest seen in more than 30 years, this flare and the resultant coronal mass ejection was luckily not directed toward Earth. NASA’s newly launched twin Solar Terrestrial Relations Observatories witnessed the event; STEREO A and B now reside along differing vantage points in Earth orbit, giving us continual views of the far side of the Sun.
4. Quebec Blackout of 1989
A large solar flare event on March 13, 1989 dramatically demonstrated the impact space weather could have. According to the NASA.gov website, “It was like the energy of thousands of nuclear bombs exploding at the same time. The storm cloud rushed out from the sun, straight towards Earth, at a million miles an hour.” The results of this X15 class monster flare hit Earth’s magnetic fields straight on and caused a widespread blackout for millions across Montreal and surrounding areas of Quebec. Neighboring electrical grids in the Northeastern U.S. barely survived blackout conditions, but minor power grid problems were noted across the U.S. One could easily see such an event cascading across the continent as an antiquated network struggles to keep up with the increased load, especially during peak demand periods such as the middle of winter or summer.
3. Halloween Flare of 2003
One of the largest solar storms ever recorded, the X45-class flare of October 2003 served as reminder of just how vulnerable we are to the whims of space weather. This flare and the subsequent coronal mass ejection damaged satellites, disrupted mobile phone communications, and forced air traffic controllers to re-route polar flights. This flare was also witnessed in dramatic fashion by the European Space Agencies’ SOHO spacecraft, and sparked aurorae that were seen as far south as Florida and Arizona.
2. Potential For Widespread Damage From Future Events
The solar minimum that marked the end of solar cycle No. 23 and the late start of No. 24 was one of the deepest and most prolonged minimums in over a century. A famous period from 1645 to 1715 where few sunspots were seen triggered a period of worldwide cooling known as the Maunder Minimum. Some scientists think that Cycle No. 24 may be intense, while others think the subsequent cycle No. 25 may disappear all together. A 2009 NASA study raised concerns about the possible catastrophic damage a large solar storm could inflict on society. A major storm could severely damage the power grid, leading to long-term power outages that could affect water and sewer operations, food distribution, transportation and communications. The alarming report concludes that in the U.S. alone, “The total economic impact in the first year alone could reach $2 trillion, some 20 times greater than the costs of a Hurricane Katrina …”
1. Carrington Super Flare of 1859
On Sept. 1, 1859, astronomer Richard Carrington recorded a white-light flare extending from a monstrous sunspot group on the Sun. But that was only the opening act of things to come. Magnetometers of the day began to twitch, and at sunset, aurorae were seen as far south as Puerto Rico. Telegraph lines overloaded, and several offices caught fire. In fact, several operators discovered they had enough ambient current to operate with their batteries disconnected, and began signaling other operators to do the same, thus avoiding damage to their equipment. Solar astronomy was just in its infancy, and the Carrington super flare marked the first time that man realized the impact that space weather could have. But what’s perhaps truly amazing is the fact that the Carrington solar storm may not have been the largest ever recorded, but a “perfect storm” that hit our magnetic field just right; one 2005 study estimated it peaked at a more pedestrian X10-class level, although we may never know for sure. History, however, is clear that it’s only a matter of time before space weather puts our modern technology to the test.