Fleeting Bright Orb Atop St. Patrick's Apex

Photo date: December 19, 2015. Photographer: Mark Mahin.

The photo below is a composite photo showing two back-to-back shots I took of a side entrance of St. Patrick's Cathedral in New York. Can you spot the difference in the photos?

The difference is that in the first photo we see a bright orb at the top of the triangular feature at the top. It isn't there in the second photo taken a few seconds later.

I find that orbs appear very, very frequently at non-random positions such as the position that we see here (at the exact top of the triangle).  See here for 144 examples of orbs appearing in similar ways, such as exactly aligning with major architectural lines or exactly aligning with the edges of flags.

There was no rain, fog, mist or precipitation on this night. The air quality listed on airnow.gov was "good," with a rating of 40.