This is a fairy ring. Pretty cool, huh. You are probably wondering how you ever survived before, in those long dreary years prior to the creation of my website without me there to point out cool stuff to you, like sunfish. You are probably bookmarking my blog and visiting every day so obsessively that you forget to change your facebook status every five minutes. Good. The world could probably use a few less Facebook statuses, though I am sure that yours are more witty and humorous than anyone else's. 
In return for all of that love and loyalty, I am going to tell you all about this mushroom picture. You are probably wondering, is it mycology or magic?

(If you don't like science, skip this next part since it will make you cry, and proceed down to the magic part. You'll know it when you see it!)

It's mycology. Sorry. The study of mushrooms. It has been determined by a higher power (i.e., some mycologist) that fairy rings are the result of the outward radial growth of a spore or a piece of mycelium. (Mycelia are basically mushroom roots. Any botanist worth their gardening shears is going to run me through with them at this point for telling you that, after politely pointing out that only plants have true roots.) Anyway, the mycelia grow out into a circle and mushrooms pop up. This can have adverse effects on the grass growing nearby, probably depending on the type of fungi forming the ring. Sometimes the mycelia grow too thick and form a layer that prevents the grass roots from getting any water. Sometimes the grass just around the mushrooms grows taller and thicker due to the nitrogen broken down and released by the fungi.

But all of that is boring, unless you happen to care like I do. So here's something we can all appreciate.
Awww, it's baby Harry taking down the Dark Lord. Cute. That brings me to the real significance of fairy circles.
Magic!
A long time ago, or not very long ago at all, or right now, depending on who you are, people believed that fairy rings were magic.
The tales vary, but one prominent belief was that a fairy ring was created wherever fairies danced in a circle. Another was that they were gateways into the kingdoms of the elves. Or they were created where a fairy appeared, or where lightning struck, or where the devil churned his butter. (I'm sure that last one brings as many questions to your mind as it does to mine. But let's stay on topic).
A human put him or herself in grave danger by stepping inside of a fairy circle. They could go blind, die young, be trapped in the circle, invisible to those outside, and be forced to dance with the fairies til they died or went mad. Fun!
(Actually, as long as there's a good deejay, that might not be a bad way to go...)
Yes, fairies were not always thought of as the nice Tinkerbell variety we don't have today. They used to not have really nasty ones.
Some optimistic folk, however, always considered fairy circles good luck. It was said that their presence guaranteed better yields from crops planted outside the circle.
As for me, I would just be excited to see one while walking in the woods one day, assuming I had woods to walk in. I might get to dance with a fairy, as long as it knows the Virginia Reel or the cha-cha. It might bring me good luck and, who knows? I might even get a few dozen likes on a Facebook status.