The surface of the sun has electrically charged gases that generate areas of powerful magnetic forces. These are called magnetic fields. The magnetic fields around the sun are constantly moving, which creates what is known as solar activity. This activity isn’t constant, but comes in cycles of varying levels. Sunspots, flares, coronal mass ejections, prominences and solar wind are all different forms of solar activity. Some of these events can even impact the Earth.
Types of Solar activity
Sunspots are areas that appear dark on the surface of the sun. They are cooler than the other parts of the surface — usually around 6,500 F — and they form in areas where magnetic fields are particularly strong.
Solar flares are a sudden explosion of energy caused by the crossing of magnetic field lines near sunspots. These eruptions release radiation into space. They are seen as bright areas on the sun and can last anywhere from minutes to hours.
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Solar flares are sometimes accompanied by a coronal mass ejection. This is a large bubble of gas and particles from the sun that explode into space at a high speed. Solar flares and CMEs are the most powerful explosions in our solar system.
A solar prominence is a large, bright feature anchored to the sun’s surface that extends outward. It forms in about a day, and stable prominences may last for several months. Scientists are still researching how and why prominences are formed.
Solar wind is a stream of electrically charged gas and particles that blows outward from the sun in all directions. It carries the sun’s magnetic field out through the solar system. Solar wind is weak compared to the wind on Earth, but it is much faster. Its speed is typically measured between 1-2 million mph.
Coronal holes appear as large, dark areas on the sun’s corona. They are associated with open magnetic field lines that allow a continuous outflow of solar wind. Coronal holes are often found at the sun’s poles and can last for weeks to months.
Solar cycle
The sun goes through cycles of high and low activity that repeat approximately every 11 years. One way to track the solar cycle is by observing the total the number of sunspots each year.
The beginning of a solar cycle is a solar minimum. This refers to a period of several years when the number of sunspots is lowest. The sun may go days without any sunspots visible. Over time, solar activity and the number of sunspots increases. A solar maximum occurs during the middle of a solar cycle when the number of sunspots is at its peak. During this time, there may be hundreds of sunspots on any given day. As the cycle ends, it fades back to a solar minimum before a new cycle begins.
Solar cycles have had number assignments since 1755 when extensive recording of solar sunspot activity began. The way to differentiate between cycles is to look at the sun’s polarity. According to Hale’s Polarity Law, sunspots switch polarities from one solar cycle to the next.
We are currently in Solar Cycle 25, which began in December 2019 after the solar minimum occurred. The solar maximum is predicted to occur sometime between November 2024 and March 2026, which is midway through the cycle. It is most likely to occur in July 2025.
Scientists considered the previous cycle, Cycle 24, to be a weak one based on the number of sunspots. The solar maximum occurred in April 2014 when sunspots peaked at 114. The average number of sunspots is 179.
Cycle 25 was also predicted to be below average in terms of solar activity. But even though we haven’t reached peak levels yet in this cycle, we have seen more activity than NASA predicted. In December 2021, there were 67 sunspots, which was more than twice the number that was expected. Solar events will continue to increase as we near the solar maximum.
Space weather
Just as the sun drives weather on Earth, it is also responsible for weather in our space environment. Space weather includes any conditions or events on the sun, in the solar wind, in near-Earth space and in Earth’s upper atmosphere that has an effect on technological systems in space and on Earth.
Effects on Earth
Earth’s magnetic field and atmosphere serve as a shield and deflect solar wind. The particles are redirected around the planet. However, when the solar wind is intense enough, some particles can leak through. These particles can trigger auroras near the poles.
Magnetic activity within the sun can sometimes cause intense solar storms. During a solar storm, solar flares and CMEs break out, sending energy through space at the speed of light. All of this extra radiation can cause damage.
Different types of space weather can affect different technology on Earth. Solar flares can interfere with radio communication. Solar energetic particles can damage satellite electronics and cause electrical failure. CMEs can disrupt electric power grids and cause outages. Geometric storms can interfere with navigation systems like GPS.
One of the best-known examples of a space weather event that impacted Earth was on March 13, 1989. Due to geomagnetically induced currents, the Hydro Québec power network collapsed. A transformer failure led to a blackout that lasted more than nine hours and affected more than 6 million people. This event was a result of a CME ejected from the sun on March 9, 1989.
Effects on other bodies
Earth isn’t the only place affected by solar wind. Unless protected by an atmosphere or magnetic field, the particles and radiation from solar wind can affect the surface of celestial bodies.
Asteroid: An asteroid has no protection around it, so solar wind can easily damage its surface. The incoming particles can kick material off into space.
Moon: Because the moon’s atmosphere is so thin, solar wind hits its surface directly with just a little bit of deflection. This deposits ingredients that could make water.
Mars: When solar wind crashes into Mars’ atmosphere, the energy creates a layer of electrified particles called an ionopause. This helps shield the surface of the planet.
Jupiter: Jupiter’s magnetic field is similar to Earth’s, but much larger. It creates a bubble that directs solar wind around the planet.
