Three alarming-looking coronal holes have appeared on the surface of the sun – as a solar storm has buffeted our planet.

But while coronal holes (which are only visible in certain wavelengths of light) look alarming, they’re actually quite common, and this week’s solar storm has been mild.

NASA says that it spotted the holes last week using its sun-watching Solar Dynamics Observatory satellite.

The SDO team says, ‘the sun featured three substantial coronal holes. Coronal holes appear as large dark areas. These are areas of open magnetic field from which high speed solar wind rushes out into space.

‘This wind, if it interacts with Earth’s magnetosphere, can cause aurora to appear near the poles. They are not at all uncommon.’

America’s Space Weather Prediction Center (SWPC) issued a G1 warning for a minor geomagnetic storm on April 10 and 11.

Coronal holes look alarming in the images captured by sun-watching spacecraft such as NASA’s sun-observing Solar Dynamics Observatory (SDO) satellite – but they’re perfectly safe, and normal.

NASA says, ‘Coronal holes are low-density regions of the sun’s atmosphere, known as the corona. Because they contain little solar material, they have lower temperatures and thus appear much darker than their surroundings.

‘Coronal holes are visible in certain types of extreme ultraviolet light, which is typically invisible to our eyes, but is colorized here in purple for easy viewing.

‘Coronal holes are the source of a high-speed wind of solar particles that streams off the sun some three times faster than the slower wind elsewhere.’