• The sun is sporting a giant coronal hole that could fit 20-30 Earths across, back-to-back.
  • Coronal holes blast rapid solar winds into space that travel 500-800 kilometers per second. 
  • The relatively-harmless winds should reach Earth by Friday for a more stunning aurora.

A giant black region on the sun, called a coronal hole, was spotted on Monday by NASA's Solar Dynamics Observatory. 

Despite the name, however, this isn't a physical hole in the solar surface. Coronal holes are cooler in temperature, so they don't glow as bright and therefore look black against the rest of the sun.

"The current coronal hole, the big one right now, is about 300,000 to 400,000 kilometers across," Alex Young, associate director for science at NASA Goddard's Heliophysics Science Division, told Insider over email. "That is about 20-30 Earths lined up back-to-back."

One Earth compared to the size of the sun. Foto: ESA & NASA

Coronal holes like these are common. There is "nothing unusual here," Scott McIntosh, a solar physicist and deputy director of the National Center for Atmospheric Research, told Insider in an email. 

Holes like this are part of the sun's normal activity. However, they're "not well understood. Their origins are unclear," McIntosh added, calling these events "the 'dark side' of solar activity."

It's worth noting that these coronal holes are the source of rapid solar winds — reaching speeds of about 500-800 km per second, Young wrote to Insider. In this case, the solar winds from this coronal hole are scheduled to reach Earth by the end of this week.

An animation of the solar wind shows particles streaming from the sun towards Earth. Foto: NASA

"We will probably start seeing the effects of the high-speed wind on March 24," Young added. "When the high-speed wind reaches Earth, the particles and the magnetic field it carries will interact with Earth's magnetic field, effectively rattling it or like ringing a bell."

More powerful magnetic fields, like from a coronal mass ejection, could cause electrical blackouts or disrupt communication technology. But coronal holes — even large ones like this — are far less violent. So the main effect to look forward to this Friday is more vibrant aurora borealis, aka northern lights. 

The Aurora Borealis (Northern Lights) is seen over the sky near Rovaniemi in Lapland, Finland, October 7, 2018. Foto: Alexander Kuznetsov/Reuters

However, we are entering a new phase of increasing solar activity where coronal holes will be less the norm and coronal mass ejections (CMEs) and powerful solar flares will become more common, Young said. 

That can be a concern since the powerful magnetic fields from CMEs and solar flares have been known to surge power grids and fry satellites. However, these events are few and far between.

In reality, Young said that for him and other solar scientists, as solar activity increases, "it's gonna get more and more exciting and interesting."

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