This is Dave Baker, a physicist at Austin College, taking videos of the spot of light from the Solstice Calendar’s gnomon holes as it moves across the floor of the IDEA Center (the science building).
At solar noon on the solstices and equinoxes, a circle/oval of light illuminates specific, very carefully marked spots on the floor of the building. Dave is the one who made the calculations.
This was an impressive feat. There is gnomon hole in the ceiling of the 3-story atrium and the light shines through it every day. 4 times a year, the light hits specific spots along a meridian line that is aligned celestial north/south, set into the terrazzo. As the building was being constructed, Dave had to consult with them about the hole, the walls, doors, and floor to get it just right. And it is perfect every time. Amazing! And that’s why he is both focused and grinning at the floor.