It is the start of the month, which means it is time for my monthly sunspot update, using NOAA’s own monthly update of its graph of sunspot activity and annotating it with extra information to illustrate the larger scientific context.

This graph is below, with the green dot showing the sunspot number for activity on the Sun’s Earth-facing hemisphere in September. As you can see, the count closely matched the April 2025 prediction by NOAA’s panel of solar scientists, which posited that the Sun was finally beginning its ramp down from solar maximum (as indicated by the purple/magenta line).


The graph above has been modified to show the predictions of the solar science community for both the previous solar maximum as well as the ongoing maximum. The green curves show the community’s two original predictions from April 2007 for the previous maximum, with half the scientists predicting a very strong maximum and half predicting a weak one. The blue curve is their revised May 2009 prediction. The red curve is the new prediction, first posted by NOAA in April 2020. At the beginning of April 2025 NOAA’s panel of solar scientists added the purple/magenta curve line, predicting that solar maximum was over, and that the ramp down to minimum had begun

I need to annotate this graph because the NOAA scientists delete their predictions as time passes, thus effectively hiding whether each prediction was right or wrong. For example, if you go to the NOAA site where this graph was obtained, you will see that the April 2025 ramp down prediction gets wiped away each month. This makes it less obvious that this prediction is not quite right, that the Sun’s activity has actually been less than predicted for the past seven months.

In a sense however these numbers validate the ramp down prediction. So far at least it appears the solar maximum has peaked, and the Sun is ramping down to solar minimum, as predicted by NOAA’s panel in April.

We must however remain cautious. As I noted in last month’s update,

It is important to note that none of the NOAA predictions for both this and last solar maximums have been correct. The Sun continues to baffle them, and this perplexity will not change until the scientists studying it finally begin to understand the fundamental processes in the Sun’s magnetic field and dynamo that produce these cycles. At the moment our knowledge is merely superficial, linking one to the other without a clear understanding of why.

It still remains possible that the sunspot activity will jump upward again in the coming months, producing a double-peaked maximum as seen in the last solar maximum from 2012 to 2014. If it does not, however, and the ramp down continues, it means this particular sunspot cycle will be another unusual one. It will be short, about ten years long, but it will also be weak. In the past 24 cycles short cycles were almost always associated with strong maximums.

The Sun’s behavior remains a mystery. We know the activity in sunspots goes through these cycles, and we know it is because its magnetic polarity flips, but we don’t know why.