The planetarium sundial A sundial, based on the design and calculations of physics professor and associate provost Brandt Kehoe, will be etched into the Downing Planetarium lobby floor. Kehoe says that sunlight coming through that circle will form a spot on the floor that moves from west to east along one of the long curves shown in the figure.
Intermediate paths are for intermediate dates a month apart.
The pattern on the floor is not symmetric because the building is oriented with its centerline 18 degrees east of north. In order to use the sundial to tell time, we need to mark the position of the spot at each hour. Kehoe explained that except at the solstices, there are two dates for each long curve and two spot locations for a given hour. These curves are called analemas. Shown in the figure are the analemas for the hours 8 a.m. to 5 p.m.