Enjoying EarthSky? Subscribe.

221,364 subscribers and counting ...

SDO peers into huge coronal hole

A NASA animation from May 17-19, 2016 shows a coronal hole in our sun’s hot outer atmosphere, or corona. Should we be scared?

Image via NASA

Our sun from May 17-19, 2016. The giant dark area on the sun’s upper half is known as a coronal hole. Image via NASA/SDO.

NASA released this animation of the sun on May 26, 2016, and it’s caused a bit of a stir around the internet, for example here and here. But there’s no need to worry (unless you’re worried about scare tactics online). The images – taken over May 17-19, 2016 by NASA’s Solar Dynamics Observatory (SDO) – show what’s called a coronal hole. If the animation makes the sun look awesomely powerful, well, that’s because the sun is.

The sun is our local star, the ultimate provider of (nearly) all of Earth’s light and heat. Each second, about 700 million tons of hydrogen in our sun’s interior are converted to about 695 million tons of helium, plus 5 million tons (=3.86e33 ergs) of energy in the form of gamma rays (source: Nine Planets). It’d be strange if all of this energy pouring from our sun’s interior just went quietly into space. It frequently doesn’t go quietly, but instead pocks the sun’s surface with sunspots, causes mighty eruptions of flares, and sometimes sends charged particles hurtling into space as coronal mass ejections.

Coronal holes are part of the ordinary activity of the sun. Even if this is the largest one in decades, as some websites have said, remember that decades – to our sun – is the blink of an eye. Our sun has been shining for billions of years, and another billion or more years will likely pass before anything truly Earth-shaking occurs.

Coronal holes like this one really are holes, of sorts. They’re low-density regions in the sun’s hot outer atmosphere, which is called its corona. The sun’s corona is that fiery halo of light seen in the brief minutes of totality during a total solar eclipse, as in the image below:

Composite image of a 2006 solar eclipse by Fred Espenak.  Read his article on the August 21, 2017 total solar eclipse, first one visible from contiguous North America since 1979.

Composite image of a 2006 solar eclipse by Fred Espenak. The white part around the black moon silhouette is the sun’s corona. Read Espenak’s article on the August 21, 2017 total solar eclipse, first one visible from contiguous North America since 1979.

NASA explained coronal holes this way:

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.

These coronal holes are important to understanding the space environment around Earth through which our technology and astronauts travel. 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.

While it’s unclear what causes coronal holes, they correlate to areas on the sun where magnetic fields soar up and away, without looping back down to the surface, as they do elsewhere.


Bottom line: Enjoy a NASA animation of a coronal hole, an awesome display of solar physics! Images from May 17-19, 2016 – via Solar Dynamics Observatory or SDO.

Deborah Byrd