Solminimum

Solminimum, or solar minimum, is the period in the approximately 11-year solar activity cycle during which sunspot numbers reach a local minimum and solar magnetic activity is at its weakest. It follows solar maximum, when sunspots and magnetic polarity reversals are most active, and precedes the next ascent toward the subsequent maximum. During a solar minimum the Sun's visible activity declines: sunspots are scarce, solar irradiance dips slightly, and the solar wind and high-energy particle emissions are weaker. The solar corona and the frequency of coronal mass ejections also decrease, producing relatively quiescent space weather conditions.

Scientists monitor solar minimum using multiple indicators, including the international sunspot number, the F10.7 cm solar radio flux, total solar irradiance, and measurements of galactic cosmic ray flux at Earth. Variability between minima exists; some minima are deeper or longer-lasting than others. Notable minima include the Maunder Minimum of roughly 1645–1715, a prolonged period with very few sunspots, and the deep minimum around 2008–2009, which followed a weak solar cycle 23.

Implications for Earth and technology are active research topics. A weaker solar magnetic shield during minima leads to higher galactic cosmic ray flux at Earth, affecting high-altitude aviation and satellites. The connection between solar minima and terrestrial climate is complex and contested, with solar forcing considered a small component relative to anthropogenic influences.