It's called a circumzenithal arc and is caused by the refraction of sunlight through ice crystals in the upper atmosphere. It's similar to a halo around the sun or moon. To see a circumzenithal ...

Social media exploded with photos of what looked like a rainbow that appeared right over the pope’s location in New York City on Friday. It was a beautiful sight, but it wasn’t a rainbow.

Thanks to Sue of Campbellsburg, IN for sending in this pic. The one at the top of this post is the close up of the circumzenithal arc and the one below is the whole picture. The sun was at the bottom.