© NASA/SDO
The sun on Sept. 22, 2019--as blank as a billiard ball.
The sun on Sept. 22, 2019--as blank as a billiard ball.
This is a sign that Solar Minimum is underway and probably near its deepest point. For 2019 overall (January through September), the sun has been blank 72% of the time, comparable to annual averages during the century-class Solar Minimum of 2008 (73%) and 2009 (71%). The current Solar Minimum appears to be century-class as well, meaning you have to go back to the beginnning of the 20th century to find lulls in solar activity this deep.
Contrary to the sound of it, "Solar Minimum" is not boring. During this phase of the solar cycle, the sun's magnetic field weakens, allowing cosmic rays to enter the solar system. This doses astronauts and possibly air travelers with extra radiation. The sun also dims, especially at extreme ultraviolet wavelengths, causing the upper atmosphere to cool and collapse. Space junk accumulates in Earth orbit as a result. Finally, streams of solar wind punch through the sun's weakening magnetic field, lashing Earth with gaseous material that can cause geomagnetic storms. (One such stream is due later this week on Sept. 27-28.)
Comment: NASA predicts the weakest solar activity in 200 years