The Blue-Green Orb and the Cross

Photo date: August 21, 2015. Photographer: Mark Mahin.

The photo below shows the back of St. Patrick's Cathedral in New York City.  At the same spot as a cross on the structure, we see an orb that seems to be green on its outside and blue in its center.

A closeup shows the unusual color structure (one I haven't seen before): green on the outside, and blue in the center.

There was no fog, mist, rain, or precipitation on this night. The air quality listed on airnow.gov was "good."