Well, seeing as I am the friend she was talking about, I can assure you it is not that. But that isn't a bad suggestion.
The ring was rather large. At first glance it refracted into almost a rainbowy glow, then solidified into a vibrant orange/red. It was a perfect circle, only being deterred by the passing clouds. Believe me when I say it was beautiful. It was like a new and remarkable quality to the already entrancing moon.
Now, I did my research and found both a scientific answer and a spiritual answer. Scientifically, it is called a lunar Corona if anyone wants to look that up to see just what we are talking about. It happens due to exactly what the previous person said about the light refracting.
The Spiritual answer means simply weather is to come. Most likely rain. But in our immediate case, snow is more likely. Celtic-wise, it means that Faery's are active our are coming into this world, and that you must be weary.
This is not to be confused with a blood moon (a red appealingly blood covered moon), which in many faiths means the coming of tragedy.
I hoped this helped the curious of mind. :)