Photo date: December 6, 2016. Photographer: Mark Mahin.
When I photographed the mysterious orb shown below against a wall about 15 feet away from me, the orb looked about as big as a beach ball (bigger than a basketball). The orb took up 11% of the original photo height. Let's do some relevant math. The length of the space just in front of a camera lens is about 10 millimeters (10,000 microns), which means the area (length times width) of the space just in front of the camera lens is about 100 million microns. But indoor suspended dust particles have a length no larger than about 10 microns, giving them an area of about 100 microns. An indoor suspended dust particle could therefore block no more than a millionth of the area just in front of the camera lens, but here we see something that took up about a hundredth of my photo area -- meaning that it was more than a thousand times too large to be explicable as a suspended dust particle.