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What happens when a giant hole opens on the sun?

NASA's Solar Dynamics Observatory has photographed a massive coronal hole gaping across the face of the sun. Here's what it means.

This image was taken in the extreme ultraviolet wavelength of 193 Angstroms, which can't be seen by the naked human eye. NASA/SDO

It sounds like something from cosmic horror: A gaping black gash opens in the face of the sun like a solar wound and lets out a stream of strange material.

Yet coronal holes aren't an uncommon phenomenon.

The shifting hole photographed by NASA's Solar Dynamics Observatory in orbit around the sun on October 10 is spectacular. At over 50 times the diameter of Earth at its widest point, it's one of the largest ever seen by the observatory.

A coronal hole isn't actually a hole in the sun. It's a comparatively colder region in the plasma aura that surrounds the sun. In X-ray and extreme ultraviolet images, these regions appear black.

Coronal holes appear most often as the sun emerges down from solar maximum, the period during sun's 11-year activity cycle during which it is most active, with sunspots and flares at peak. The most recent solar maximum peaked in 2014. The minimum, with few sunspots and flares, is expected around 2019.

The hole is a region that is low in energy and gas. This causes the magnetic fields to fall away from those regions, resulting in lower density plasma. This, in turn, allows high-speed solar winds to escape from the sun. When these blast toward the Earth, they result in geomagnetic storms.

When the solar wind collides with the Earth's magnetosphere, the magnetic field of the solar wind and the Earth's magnetic field interact, and a transfer of energy occurs. This creates one of Earth's most spectacular phenomena: the aurora, a light show that danced across the sky.

Coronal holes typically last for several months, shifting around the surface of the sun, changing shape. The hole photographed on October 10 formed from three smaller holes that were observed on October 8. These holes were responsible for an incredible aurora show photographed in Norway.

Geomagnetic storms can cause a few problems for humans on Earth. The particle activity in the magnetosphere can interfere with radio and radar communications, as well as GPS devices.

Interestingly, they also interfere with animals' navigational abilities. Homing pigeons, for instance, navigate poorly during geomagnetic storms, since the storms disrupt the magnetic fields that the pigeons use as a guide. Whales can also beach themselves in large numbers.

The coronal hole is still hanging around, though now only smaller holes are visible. The National Oceanic and Atmospheric Administration is forecasting aurora across Canada, Greenland, northern Russia and northern Scandinavia. If you're lucky enough to live in any of those areas, get your camera ready.

You can also check out what the sun is doing at any point in time on the Atmospheric Imaging Assembly website.