For most of human history, the sun appeared to be stable. It was a stoic stellar presence that went about its business outside of our awareness of fusing hydrogen into helium and helping to keep Earth habitable. But in our modern technological age, that façade has disappeared.
We now know that the sun is controlled by its strong magnetic fields, and as these fields go through their changes, the sun becomes more active. According to NASA, the Sun is currently at its solar maximum, a time of increased activity.
Solar Maximum means pretty much what it sounds like. In this phase of the cycle our star shows maximum activity. The Sun's intense magnetic fields are producing more sunspots and solar flares than ever before in its 11-year cycle.
The solar maximum is based entirely on the sun's magnetic fields. These fields are measured in Gaussian units, which describe the magnetic flux density. The sun's poles measure about 1 to 2 Gauss, but sunspots are much higher at about 3,000 Gauss. (Earth is only 0.25 to 0.65 gauss at its surface.) Because the magnetic field is much stronger where sunspots occur, they inhibit convective heating from deeper within the sun. This causes sunspots to appear as dark spots.
Sunspots are visual indicators of the Sun's 11-year cycle. The National Oceanic and Atmospheric Administration and an international group called the Solar Cycle Prediction Panel monitor sunspots to understand where the sun is in its cycle.
“During solar maximum, the number of sunspots and therefore the amount of solar activity increases,” said Jamie Favours, director of the Space Weather Program at NASA Headquarters in Washington. “This increase in activity provides an exciting opportunity to learn more about our nearest star – but also has real implications for Earth and throughout our solar system.”
The implications have become clear for many of us recently. In May 2024, the Sun launched several CMEs. When the magnetic fields and charged particles reached Earth, they triggered the strongest geomagnetic storm in 200 decades. This created colorful auroras that were visible much further from the poles than usual. According to NASA, these auroras were probably among the most powerful phenomena in the last 500 years.
Scientists know that the sun has reached its solar maximum. But it takes a whole year. They don't know when activity peaks until they've watched it for months and the activity has waned.
“This announcement does not mean that this is the peak of solar activity we will experience this solar cycle,” said Elsayed Talaat, director of space weather operations at NOAA. “While the Sun has reached solar maximum, the month in which solar activity on the Sun peaks will not be identified for months or years.”
Each cycle is different, making it difficult to characterize maximum solar activity. Different peaks have different durations and peak higher or lower than others.
It is important to understand the Sun's cycle because it creates space weather. During solar maximum, increased sunspots and solar flares also lead to more coronal mass ejections (CMEs). CMEs can hit Earth, and when they do, they can trigger auroras and cause geomagnetic storms. CMEs, which are clumps of hot plasma, can also affect satellites, communications and even power grids.
NASA's Solar Dynamics Observatory captured these images of solar flares below, as seen in the bright flashes in the left image (May 8, 2024 flare) and the right image (May 7, 2024 flare). The image shows 131 angstroms of light, a subset of the extreme ultraviolet light that highlights the extremely hot material in flares and is colored orange.
via GIPHY
During solar maximum the sun produces an average of three CME per day, while during solar minimum it drops to one CME every five days. Most concerning is the impact of CMEs on satellites. In 2003, satellites experienced 70 different failures. The failures ranged from faulty signals in a satellite's electronics to the destruction of electrical components. The 2003 solar storm was blamed for 46 of these 70 outages.
CMEs also pose a danger to astronauts orbiting Earth. The increased radiation poses a health risk and during storms, astronauts seek safety in the most shielded part of the ISS, Russia's Zvezda service module.
Galileo and other astronomers noticed sunspots hundreds of years ago, but didn't know exactly what they were. In a 1612 pamphlet entitled “Letters Concerning Sunspots,” Galileo wrote: “The sun, turning on its axis, carries it about without necessarily showing us the same spots, in the same order, or in the same shape. This contrasted with the views of others about the spots, some of which suggested they were natural satellites of the Sun.
We have known about the Sun's magnetic fields for 200 years, although scientists initially did not know that magnetism came from the Sun. In 1724, an English geophysicist noticed that his compass was behaving strangely, deviating from the magnetic north pole throughout the day. In 1882, other scientists linked these magnetic effects to an increase in sunspots.
Over the past few decades, we have learned much more about our stellar companion thanks to space probes dedicated to its study. NASA and ESA launched the Solar and Heliospheric Observatory (SOHO) in 1995, and NASA launched the Solar Dynamics Observatory (SDO) in 2010. In 2011, we got our first 360-degree view of the Sun thanks to NASA's two Solar TERrestrial RElations Observatory (STEREO) spacecraft. In 2019, NASA launched the Parker Solar Probe, which is also humanity's fastest spacecraft.
Our understanding of the sun and its cycles is now far more complete. The current cycle, Cycle 25, is the 25th since 1755.
This figure shows the number of sunspots over the last twenty-four solar cycles. Scientists use sunspots to track the progress of the solar cycle; The dark spots are associated with solar activity, often as the origin of giant explosions – such as solar flares or coronal mass ejections – that can hurl light, energy and solar material into space. Photo credit: NOAA's Space Weather Prediction Center
“Sunspot activity in solar cycle 25 has slightly exceeded expectations,” said Lisa Upton, co-chair of the Solar Cycle Prediction Panel and senior scientist at the Southwest Research Institute in San Antonio, Texas. “While there have been some large storms, they are no larger than what we would expect in the maximum phase of the cycle.”
The strongest flare so far in Cycle 25 occurred on October 3, when the Sun emitted a class X9 flare. However, scientists believe there will be more outbreaks and activity. Even in the downturn phase of the cycle, very strong storms can occur, but they are not as frequent.
On October 3, 2024, the sun emitted a powerful solar flare. As of this writing, this solar flare is the largest of solar cycle 25 and is classified as an X9.0 flare. The X class denotes the most intense flares, while the number provides further information about their strength. NASA's Solar Dynamics Observatory captured images of this solar flare on October 3, 2024 – as seen in the bright flash at the center. The image shows a mixture of 171 angstroms and 131 angstroms of light, subsets of extreme ultraviolet light.
Photo credit: NASA/SDO
The Sun's 11-year cycle is just one of its cycles, which are nested within larger cycles. The Gleissberg cycle lasts between 80 and 90 years and modulates the 11-year cycle. The De Vries cycle or Suess cycle lasts between 200 and 210 years, the Hallstatt cycle around 2,300 years. Both cycles contribute to long-term solar variation.
But despite everything we know about the sun, there are huge gaps in our knowledge. The sun's magnetic poles change on an 11-year cycle, and scientists aren't sure why.
There is still much more to learn about the sun, but we won't have enough time to study it any time soon. It is in the middle of its 10 billion year lifespan and will be a main sequence star for another five billion years.
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