The solar cycle
The Sun's roughly 11-year cycle, where Solar Cycle 25 is now, and what to expect over the next few years.
The Sun's activity rises and falls over about 11 years. At solar minimum there are few or no sunspots for weeks; at solar maximum there are many, with frequent flares and CMEs. The count of sunspots, the sunspot number, is the standard measure.
Solar Cycle 25
The current cycle, the 25th since records began in 1755, started in December 2019. NASA, NOAA and the international Solar Cycle Prediction Panel announced in October 2024 that the Sun had reached its maximum period. The Royal Observatory of Belgium, which keeps the official sunspot record, later confirmed that the smoothed sunspot number peaked in October 2024 at about 161, well above the 105 to 125 originally predicted. That made it a stronger cycle than the one before.
What to expect now
The Sun is now in the declining phase. That doesn't mean the end of aurora:
- Big storms still happen in the years after maximum. Some of the strongest storms in past cycles came during the decline.
- Coronal holes become more common, bringing regular, recurring fast wind and frequent moderate aurora at high latitudes, often about 27 days apart.
- Fewer extreme storms reach very low latitudes as the decline continues towards the next minimum, which, if this cycle runs to an average length, would be around the end of the decade.
Seasons matter too
Whatever the cycle is doing, geomagnetic activity tends to be higher around the equinoxes, in March and September. The usual explanation, the Russell–McPherron effect, is that Earth's tilt then lines its magnetic field up better with the solar wind's southward field. Combined with long dark nights, late September to October and late February to March are good times to watch.