March 1, 2019: There are 28 days in February. This year, all 28 of them were spotless. The sun had no sunspots for the entire month of Feb. 2019. This is how the solar disk looked every day:
The last time a full calendar month passed without a sunspot was August 2008. At the time, the sun was in the deepest Solar Minimum of the Space Age. Now a new Solar Minimum is in progress and it is shaping up to be similarly deep. So far this year, the sun has been blank 73% of the time–the same as 2008.
Solar Minimum is a normal part of the solar cycle. Every ~11 years, sunspot counts drop toward zero. Dark cores that produce solar flares and CMEs vanish from the solar disk, leaving the sun blank for long stretches of time. These minima have been coming and going with regularity since the sunspot cycle was discovered in 1859.
However, not all Solar Minima are alike. The last one in 2008-2009 surprised observers with its depth and side-effects. Sunspot counts dropped to a 100-year low; the sun dimmed by 0.1%; Earth’s upper atmosphere collapsed, allowing space junk to accumulate; the pressure of the solar wind flagged while cosmic rays (normally repelled by solar wind) surged to Space Age highs. All these things are happening again.
How does this affect us on Earth? The biggest change may be cosmic rays. High energy particles from deep space penetrate the inner solar system with greater ease during periods of low solar activity. Indeed, NASA spacecraft and space weather balloons are detecting just such an increase in radiation. Cosmic rays can alter the flow of electricity through Earth’s atmosphere, trigger lightning, potentially alter cloud cover, and dose commercial air travelers with extra “rads on a plane.”
As February ended, March is beginning … with no sunspots. Welcome to Solar Minimum!