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The Sun did not switch on after decades of being dormant. A 2025 study found that a multi-decade weakening trend in several solar-wind and magnetic-field measurements near Earth ended in 2008, and that those fitted values rose between 2008 and 2025. The researchers do not yet know why the reversal happened or whether it will continue.
What does “the Sun is waking up” mean?
“Waking up” is a metaphor, not a technical diagnosis. It comes from Jamie Jasinski, the NASA Jet Propulsion Laboratory researcher who led the study with Marco Velli. Jasinski said the reversal was a surprise after signs had pointed toward a prolonged period of low activity. The study itself describes changes in the solar wind and its associated magnetic field—not a uniform increase in every measure of solar activity.
The solar wind is a stream of charged particles flowing outward from the Sun. The researchers analyzed measurements taken at 1 astronomical unit, roughly Earth’s distance from the Sun, using heliospheric observations that include data from NASA’s ACE and Wind missions. Their paper, “The Sun Reversed Its Decades-long Weakening Trend in 2008,” was published in The Astrophysical Journal Letters in 2025.
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Which solar-wind measurements increased?
The study reports changes in fitted trends comparing 2008 with 2025. These percentages describe relative changes in the measured parameters; they are not forecasts or percentages of the Sun’s total energy output.
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| Measured parameter | Reported fitted-trend change, 2008–2025 |
|---|---|
| Solar-wind proton speed | About 6% increase |
| Solar-wind proton density | About 26% increase |
| Solar-wind proton temperature | About 29% increase |
| Thermal pressure | About 45% increase |
| Mass flux | About 27% increase |
| Momentum flux, or dynamic pressure | About 34% increase |
| Energy flux | About 40% increase |
| Interplanetary magnetic-field magnitude | About 31% increase |
| Radial component of the interplanetary magnetic field | About 33% increase |
The different percentages matter: the reported change was not the same for every parameter. In particular, a 45% increase in thermal pressure does not mean the Sun as a whole became 45% more powerful.
Is this the same as Solar Cycle 25 reaching its maximum?
No. The study’s multi-decade trend and the roughly 11-year solar cycle describe different timescales and indicators. The study tracks solar-wind and magnetic-field parameters; the familiar cycle is commonly followed through sunspots and its phases of rising and falling magnetic activity.
| Long-term trend in the study | Solar Cycle 25 | |
|---|---|---|
| Timescale | Multi-decade change, with the weakening trend ending in 2008 | A recurring cycle of roughly 11 years |
| What is being described | Solar-wind and associated magnetic-field measurements near Earth | A cycle phase commonly tracked through sunspots |
| What the finding establishes | A reversal in fitted trends across the study’s measured parameters | A phase in the recurring cycle |
Solar Cycle 25 began at the solar minimum in December 2019. In October 2024, NASA and NOAA announced that the Sun had reached the cycle’s maximum phase. That announcement did not identify the exact month of the peak: scientists can confirm a peak only after they observe a consistent decline afterward.
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Does the reversal mean more solar storms?
Greater solar activity can coincide with more frequent space-weather events, but this study does not predict a particular storm or show that the long-term reversal caused any specific event. Flares and coronal mass ejections can affect conditions around Earth; the May 2024 geomagnetic storm, described by NASA as the strongest at Earth in two decades, is an example of a space-weather event, not proof of a cause-and-effect link to this trend.
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Space weather can affect satellites and astronauts, radio and GPS communications, and power grids. Solar-cycle forecasts help estimate event frequency and inform sectors such as satellite operations, but a broad trend is not a substitute for event-specific forecasts. NOAA notes that the newest six months of observed indices on its data page are preliminary, so recent displayed values should not be mistaken for finalized historical measurements.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why did the trend reverse, and will it continue?
The study reports observed associations and fitted trends; it does not establish the physical cause of the post-2008 reversal. Nor does it show that the rise will persist indefinitely. The authors say continued measurements are needed to determine whether the parameters keep rising in future cycles or stabilize.
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