The Sun's 25th cycle is here.
Every 11 years, the Sun begins a new solar cycle, marked by periods of violent eruptions and magnetic explosions that send flashes of radiation into space.
The new solar cycle began in December 2019. On Tuesday, NASA and the National Oceanic and Atmospheric Administration (NOAA) announced it will be similar to the last cycle. Considered relatively calm, that cycle included the weakest solar maximum since 1928.
Calm or not, the new solar cycle will still impact life on Earth, as well as future space voyages.
This is Solar Cycle 25 because the numbering of cycles began in 1755. Although it began in December 2019, it takes up to 10 months for scientists to determine when the new cycle actually began since the Sun is a variable star.
“As we emerge from solar minimum and approach Cycle 25’s maximum, it is important to remember solar activity never stops; it changes form as the pendulum swings,” Lika Guhathakurta, a solar scientist at the Heliophysics Division at NASA Headquarters in Washington, said during a press briefing on Tuesday.
The Solar Cycle 25 Prediction Panel, an international team of experts on the Sun, agreed that the next solar cycle will be similar to the last one. This may mean the end of a weakening solar cycle trend, with each cycle exhibiting less activity than the one before it.
For the past 50 years, around four solar cycles or so, the Sun has been unusually active. The year 2019 saw an unusually low number of sunspots, with a total of 281 days where there were no sunspots on the Sun.
This caused some speculation, and a bit of panic, that the Sun would undergo another Maunder minimum, a period between 1645 and 1715 where reduced activity was paired with a severe drop in temperatures in the Northern Hemisphere.
However, the team of experts is hopeful about cycle 25.
“It’s hard to pin down a specific date, but we predict that the middle of 2025 is when we’ll have the most sunspots of this cycle," Gordon Petrie, a researcher at the National Science Foundation’s National Solar Observatory, and member of the Prediction Panel, explained during the press briefing.
"We expect there to be approximately 115 sunspots at the maximum, which is very close to what we saw during the previous cycle, which maxed out at 120 sunspots," he added.
"This is what tells me that this might be the beginning of a return to stronger solar cycles and break from ever-shrinking ones we have seen the past few decades.”
What is a solar cycle?
Solar activity largely depends on the Sun's magnetic field. The Sun’s magnetic field goes through a periodic cycle in which the south and north poles essentially switch spots, and it takes another 11 years or so for them to switch back.
The solar cycle is measured by changes in the Sun's activity. The Sun periodically ejects boiling-hot plasma, in the form of solar flares and solar wind, across the Solar System.
The Sun's activity starts increasing halfway through the cycle, meaning more solar flareups and outflow of radiation from our host star. As the solar cycle winds down, the Sun becomes less active.
Its activity, meanwhile, is measured by its sunspots — dark spots that mark the Sun's surface. Sunspots are caused by the magnetic field inhibiting the transfer of energy on the surface of the Sun through the process of convection, where hot fluid rises and cooler fluid sinks.
Sunspots are, in turn, an indication of solar activity. As the Sun reaches its 'solar maximum,' the most amount of sunspots can be seen across its surface. When the solar cycle comes to an end, there are fewer and fewer sunspots, a period known as 'solar minimum.'
How does the Sun affect space weather?
Space weather is controlled by the flareups of the Sun that are ejected into outer space. The Solar Cycle 25 Prediction Panel notes that just because it is a relatively calm solar cycle, doesn't mean we should not expect to see a few flare-ups of solar activity as the cycle heats up.
The Sun is an active star, periodically subject to events like coronal mass ejections, high-speed solar wind, and solar flares. Solar flares are seen as bright areas on the Sun — they're an intense burst of radiation, linked to magnetic energy associated with sunspots. These ejections can cause magnetic storms in the Earth's upper atmosphere, which can affect power grids, satellites, and orbiting spacecraft and astronauts.
NASA and NOAA have been working together to enhance predictions of space weather, and improve our preparedness for it.
“There is no bad weather, just bad preparation,” Jacob Bleacher, chief scientist for NASA’s Human Exploration and Operations Mission Directorate at the agency’s Headquarters, said at the press briefing. “Space weather is what it is, our job is to prepare.”
As NASA prepares to return humans to the Moon through its upcoming Artemis mission, it has become more crucial to mitigate the effects of space weather and radiation on astronauts during longer spaceflights. To prepare, the space agency has sent out missions to the Sun, like the Solar Orbiter, to better understand solar activity, and be able to better predict it in the future.
Meanwhile, NOAA runs the Space Weather Prediction Center in Boulder, Colorado, which monitors the Sun and forecasts its activity.
“Just as NOAA’s National Weather Service makes us a weather-ready nation, what we’re driving to be is a space weather-ready nation,” Elsayed Talaat, director of Office of Projects, Planning, and Analysis for NOAA’s Satellite and Information Service, said during the briefing.
The next solar maximum is predicted for July 2025. Scientists are eager for the opportunity the maximum will allow for further study of the Sun.
“We hope that an eclipse close to solar maximum will not only show us an awe-inspiring corona but also some big, interesting sunspots on the face of the Sun to help us learn about living inside the atmosphere of an active star and the space weather it creates,” Valentin Martinez Pillet, director of the National Solar Observatory, said during the press briefing.