Does the Sun sleep?
The Sun does not always burn at the same intensity. Roughly once every eleven years it draws a breath — swinging from calm to fury and back to calm.
Scientists have established that the Sun raises and lowers its activity over the years. This roughly 11-year cycle is called the solar cycle. At the start of the cycle the Sun emerges from its slumber, reaches its most active state between years 5 and 8, then grows quiet again — and swaps its north and south poles.
The Sun's activity rises and falls on an ~11-year rhythm. Near maximum, sunspots and solar storms are frequent and the aurora reaches far south; near minimum, quiet nights can pass with nothing at all. Solid: the 13-month smoothed sunspot number; faint: monthly means; dashed: a model past the record.
Solar maximum.
The cycle's most active phase is called the solar maximum. The most striking auroras are most likely in this phase. Cycle 24 peaked in 2014–2015 and ended in early 2020; a sunspot in April 2020 was counted as the onset of cycle 25. Even in the quiet phase — as long as the Sun exists — auroras keep appearing.
In a year close to the solar maximum of cycle 23, a great flare on 4 November 2003 released an immense amount of electrical energy. Had it occurred on the face of the Sun turned toward Earth, it could have caused severe damage to sensitive electronics — a reminder that the solar maximum is not only a visual feast but also a window of risk.
- +Declining phase · strongest years ahead
- +Cycle 25 peak · stronger than forecast
- ○Original · book edition