The Washington PostDemocracy Dies in Darkness

The sun has ‘gone blank’ for the second time this month. Here’s what that means.

The blank sun through four different filters. (NASA)

The sun is blank for the second time in less than a month — not a single dark sunspot mars its surface. It’s a sign our star is entering a new period of decreased activity — one that will continue to last for about five years. But, despite the overall decline, history has proven that some of the largest solar storms in memory can occur when sunspots appear to be ebbing.

The sun is a volatile star. Its surface changes on a 11-year solar cycle that oscillates between periods of increased and decreased sunspot production. Sunspots are dark areas on the surface of the sun that indicate intense magnetic activity — so strong, in fact, that it inhibits solar convection and thus reduces the temperature of the sun in that location. Sunspots can be just a few miles wide, but the largest can span 100,000 miles in diameter, or more than 12 Earths across. These massive spots can be seen on the surface of the sun without a telescope, and they can be just half as hot as their surroundings.

Sunspots are not just something for scientists to observe and track; their fluctuating existence has huge implications for our environment and technology here on Earth.

Could a weakening sun cancel global warming? No.

Sunspots are simply the observable sign of strong solar magnetic fields. Sometimes they are stable, and other times they are explosive. These reservoirs of strong magnetic field can fuel solar flares and coronal mass ejections that lead to radiation storms and geomagnetic storms on Earth that have the potential to drop-kick our modern way of life back to the stone age. It is a space weather forecaster’s job to determine if and when these storms will arrive so that — with enough warning — we can implement safeguards on our technology to prevent failure and lasting damage.

Video by NASA’s Solar Dynamics Observatory shows an active region near the right-hand edge of the sun’s disk, which erupted with at least a dozen minor events over a 30-hour period from Nov. 3-5, 2015. (Editor's note: This video does not contain audio.) (Video: Video/YouTube)

After an activity maximum in the early 2000s, our star is entering a solar minimum. Slowly but surely, the number of shadowy spots on the surface of the sun will decrease.

But that doesn’t mean it will go silent.

This period of sunspotlessness will last for a few days, but eventually the periods will span for weeks and then perhaps months. Right now, the side of the sun that faces Earth is currently clear of sunspots, but the opposite side is not.

Something erupted on the far side on Saturday that jettisoned a massive cloud of plasma into space, noted “Within a few days, the underlying blast site should reveal itself as the sun’s rotation brings the active region over the horizon,” wrote. “We shall see if it is a large sunspot or something less threatening.”

We have plenty of reason to believe that, despite the waning solar activity, something large could still be looming. The oft-cited “Carrington Event” in 1859 occurred during a relatively weak solar cycle. This massive geomagnetic storm was one of the largest ever recorded. It spawned aurorae as far south as the Caribbean. If a storm of this magnitude occurred today, it could wipe out electricity, Internet and all of the technology that relies on those things for weeks or even months across an entire continent.

The sun is well into the declining phase of the current Cycle 24, and it is likely to reach the minimum around 2020. But it’s not too soon to think about the next cycle, which will begin around 2020.

This is still the hardest space weather problem, and it’s a huge threat to our infrastructure

Space weather forecasters are already thinking about the next solar cycle and wondering what it will bring. The smart money is predicting a small cycle. A reasonable expectation is that the sun’s polar magnetic fields will continue to increase over the next five years, boding well for a Cycle 25 that is at least as large as the current cycle.

Not only is it an interesting question from a science perspective, but most important, the magnitude of the cycle dictates the impacts to critical infrastructure and human activities.

Tracking sunspots: An astronomer’s favorite pastime, even in the Middle Ages

Radiation from space is a key issue in manned spaceflight — read: a manned mission to Mars — satellite performance and even the radiation passengers and aircrew receive on polar flights. Plus, business jets typically fly at a higher altitude, and radiation dose is a function of altitude. The dose varies with the intensity of the solar cycle.

Large eruptions of radiation from sunspots are most common during solar maxima, but there’s another kind of radiation that reaches Earth during solar minima. Galactic cosmic rays — or the ambient radiation from space — are even more abundant during the sun’s inactive periods, when big solar storms are not available to “shield” the Earth from the galaxy’s radiation. During solar minimum, that shielding goes away, and galactic cosmic rays have much greater access to our planet.

This is reason alone to keep our solar guard up, even as sunspots fade.