For centuries, ancient civilizations worshipped the sun as holy. However, occasionally the sun is just hole-y. Literally. The sun can get something called a coronal hole, which looks like a huge black spot on the sun. As ominous as that sounds, it’s not anything to be worried about, though.
You won’t be able to see these holes, because they can only be viewed with instruments that can sense heat, or infrared cameras. But NASA has something called the Solar Dynamics Observatory (or SDO) up in space, which keeps an eye on the sun and its changing condition. And this spacecraft can send the infrared photos that will allow us to see phenomena like solar holes.
Images from the SDO are often colored in order to make the effect easier to see. Techonology enthusiasts such as Tom Yulsman can also use the images from NASA to make composite images that show the movement and scope of the coronal hole.
The easiest way to understand a complicated term like coronal hole is to break it down. The corona is an astronomy term for the outermost layer of the sun. So a coronal hole means that there’s a hole in the layer of hot gasses that form the outside of the sun.
How a hole forms
If you know anything about gasses, you know that they like to expand. So what keeps all of the gasses in the sun within a concentrated space? The answer is magnetic fields. Usually the magnetic field lines around the sun form loops, keeping the majority of the gasses contained (of course there’s always some gas that escapes. We’ll get to that later). When a coronal hole happens, the magnetic field distorts, and the magnetic lines point out into space. This means that more of the gas from the sun can flow into space.
When the hot gas flows out into space, the area that it used to occupy has less gas in it. This also means that the temperature of that area is (relatively) lower, and that the area looks darker than the other parts of the sun, which still have a lot of the burning gas. This is why the coronal holes appear black in comparison with the rest of the sun.
What are the impacts?
As previously mentioned, there is always some gas that escapes from the sun. This normal leakage of gas is called a solar wind. But when a solar hole occurs a lot more gas flows out than the normal rate. In fact, NASA stated in an earlier article about coronal holes that solar winds can leave a hole at a rate that’s three times faster than the average rate. Another space information site says that coronal winds normally leave the sun at about 250 miles/second, but that they can leave the sun at 500 miles/second when the magnetic fields are weaker and there is a coronal hole.
So extra strong cosmic winds in can’t have no effect at all right? We’re far enough away from the sun that the heat won’t damage Earth. But the extra solar material creates something called a geomagnetic storm. These storms add extra heat to earth’s atmosphere, which changes the overall composition, and can interfere with devices that we’ve put in the lower atmosphere. So this means satellites, radio waves and GPS signals may all be thrown slightly off. It may also change the magnetic currents that flow through power grids and pipelines.
If you would like to watch for a coronal hole over time check out NASA’s SDO website.