June 21, 2019: The sun is blank–really blank. No sunspots have appeared for the past 34+ days, giving the sun the appearance of a giant orange billiard ball. This is a sign that Solar Minimum is underway. Earlier this year, a panel of experts from NOAA and NASA predicted that the solar cycle would reach its nadir sometime between July 2019 and Sept 2020. The current stretch of spotless suns is consistent with their forecast.
Above: The sun on June 21, 2019. Credit: NASA’s Solar Dynamics Observatory
What happens when sunspots vanish? For one thing, solar flares stop happening. No big explosions means no shortwave radio blackouts and fewer geomagnetic storms. Also, the sun dims. Sunspots are sources of extreme ultraviolet radiation (EUV). Without sunspots, EUV levels decrease, causing Earth’s upper atmosphere to cool and contract. Satellites and space junk stay in orbit longer as aerodynamic drag subsides.
During this phase of the solar cycle, the solar wind slows and the sun’s magnetic field weakens–shields down! This allows extra cosmic rays from deep space to penetrate the solar system. Indeed, recent high altitude balloon flights show increased radiation in Earth’s atmosphere. Extra cosmic rays can trigger lightning, alter the electro-chemistry of the upper atmosphere, and boost dose rates on commercial airplane flights.
Solar Minimum won’t last forever. Forecasters expect sunspot numbers to increase after 2019-2020, climaxing in a new Solar Maximum around 2023-2026. Meanwhile, stay tuned for more blank suns.