SILSO, the World Data Center for the production, preservation and dissemination of the international sunspot number, has just released the sunspot numbers for December 2025. The sunspot number is the number of sunspot groups multiplied by 10 to which then the number of individual sunspots is added. The -provisional- monthly sunspot number for December is 124.0, which is up from the preceding 2 months. The overall trend remains declining. This is shown in the graph underneath, with the daily sunspot numbers in yellow, the monthly numbers in blue, and the smoothed (nearly "13-month averaged"; see the FAQ page for more details) sunspot numbers in red. The dashed red lines show the expected evolution, based on different models.
The Sun showed us two different faces during December. During the middle of the month, only few sunspots were visible with the daily sunspot number around 60-70. However, during the beginning and end of the month, the sunspot numbers were relatively high and around 180 and 150 respectively. This varying sunspot activity can be seen in the solar pictures underneath, taken by the solar telescopes in Uccle (USET) on resp. 4, 15 and 28 December. Some of the smudges are due to passing clouds. Using eclipse glasses, the largest sunspots were visible to the protected naked eye - in particular during the days around 5 December. The first week of December also saw 2 X-class flares: an X1.9 on 1 December, and an X1.1 on 8 December. The last week of December saw compact sunspot groups, but with little complex magnetic structures resulting in only medium-class flares.
