The Beginning of the Next Solar Cycle as the Current One Continues

The Next Solar Cycle Has Started… But the Current One Hasn’t Finished Yet

We may be already seeing the makings of the next solar cycle, peeking out through the current one. It’s been an eventful journey so far. Solar Cycle Number 25 has been one of the strongest cycles in recent memory, producing several massive sunspot groups. The current large region turned Earthward (Active Region 3780) is now easily visible with eclipse glasses, with no magnification needed. Cycle 25 officially started back in 2019.

To be sure, the latest solar cycle will be one for the history books as it heads towards an active maximum in 2025. However, even though Cycle 25 will extend through the remainder of the current decade, there are already signs that Cycle 26 could be beginning, just under the roiling solar surface. A study out of the University of Birmingham recently presented at the Royal Astronomical Society’s National Astronomical Meeting in Hull, United Kingdom, shows that key indicators for the start of the next cycle may already be in place.

Numbering the solar cycle under the current convention dates all the way back to the start of Cycle 1 in 1755. The pattern for numbering cycles was established in 1852 by astronomer Rudolf Wolf. A new solar cycle officially begins when sunspots appear at higher solar latitudes and typically have a reversed polarity compared to the previous cycle. These spots then make their way down near the solar equator as the cycle progresses. Furthermore, spots from two cycles can also mix as the transition period unfolds.

Laying out spots from successive cycles versus latitude creates a butterfly diagram that showcases this effect, known as Spörer’s Law. However, there is more to the Sun than meets the eye. As a large ball of hydrogen and helium gas, the Sun does not rotate as a single solid mass; instead, it rotates faster at the equator (25 days) compared to near the poles (34 days). Scientists can delve into the solar interior through a method known as solar helioseismology, which observes waves crossing the solar photosphere in an attempt to model the interior.

These internal sound waves form bands in a phenomenon called solar torsional oscillation, with faster-rotation belts serving as a harbinger of the next cycle. These faster-rotating bands move along with visible sunspots towards the solar equator as the cycle progresses. Rachel Howe from the University of Birmingham states, “The indication of Cycle 26 that we see is that the solar rotation has been speeding up at around 50 degrees latitude and now appears to be leveling off.”

The Global Oscillation Network Group (GONG) makes the science of helioseismology possible through a worldwide network that monitors the Sun continuously. Space-based instruments like the Helioseismic Magnetic Imager aboard the joint ESA/NASA Solar and Heliospheric Observatory (SOHO) complement this effort. This continuous monitoring effort dates back to 1995, covering the last three solar cycles and providing insights into the start of Cycle 26.

Solar Cycle 25 has been exceptionally active, surpassing expectations and following the historic lull between Cycles 24 and 25. The profound minimum during this downtime saw few sunspots, aligning with predictions of a stronger cycle on the rebound. Looking ahead to Cycle 26, Howe notes, “The Sun is always surprising,” highlighting key discoveries from spacecraft like Solar Orbiter and Parker Solar Probe that provide unprecedented insight into the connections between the Sun’s surface and space weather events that impact Earth.

The recently observed solar storm on May 10th was one of the most impressive of the cycle, sending aurora to latitudes as far south as Spain and Mexico—an occurrence rarely seen in those regions. As we continue to monitor the Sun and its cycles, we aim to better understand and predict the behavior of our tempestuous star.

Historically, the Wolf Sunspot Number serves as a gauge of solar activity, while the orientation and strength of the heliospheric current sheet are suggested to be a better indicator of the current solar cycle’s health. The Sun’s magnetic field flips every 11 years, returning to the same relative orientation every 22 years. This cyclical nature is a source of fascination and study for astronomers as they aim to unravel the mysteries of our closest star.

In conclusion, the ongoing observation and study of solar cycles provide valuable insights into the behavior of our Sun and its impact on Earth. As we embark on the journey into the next solar cycle, scientists continue to monitor and analyze the intricate patterns and phenomena occurring on our dynamic star.