Solar eclipse glasses can actually be used to see cool sun features otherwise hidden in plain sight.
If you haven’t gotten rid of, or donated your solar eclipse glasses, you’ll want to hang onto them for more than just the next eclipse. It turns out, you can actually use the glasses to spot a common — yet fascinating — feature of the sun.
As NASA pointed out, when magnetic fields rise up from below the sun’s surface, they eventually poke through, creating cool, dark patches on the sun.
Related: When Is the Next Eclipse?
Since these sunspots, which look like tiny little freckles covering the face of the sun, are darker than the rest of the bright solar disk that surrounds them, those with solar eclipse glasses can use them to safely check out the sight.
Sunspots can be seen for up to two weeks before starting to fade or rotate out of view, according to NASA, giving viewers a good amount of time to catch the phenomenon, which can often point to solar activity that includes solar eruptions, like flares.
Your eclipse glasses can also be used to see another feature that’s often hidden to the naked eye, known as limb darkening. This optical effect happens when you look directly at the center of the sun.
When the center of the sun appears to be significantly brighter than the edge, you are experiencing limb darkening.
The way limb darkening works is that when you look at the center of the sun, you have an unobstructed view of the warm and bright base of the photosphere, but as you start to look towards the edges, the sun's curvature makes it so that you can only see the upper layers of the photosphere. These upper layers are cooler and emit less light, so they appear darker than the bright center, as NASA explained.
While NASA also noted that the sun is steadily moving toward a period of lower solar activity, the sun recently released two powerful solar flares, the second of which was the most powerful in more than 10 years as a result of sunspots, according to Space.com.