Wooster Hall at SUNY New Paltz has a neat feature.   The main staircase is exactly aligned along a north-south line, and skylight windows in the ceiling were placed so that light from those windows lines up at the bottom of the staircase at solar noon on the equinoxes.    In the summer the sun is higher, and so the light from the skylights lines up with the top stairs of the staircase.     It’s become an event on campus to come watch the lights slowly crawl over until they line up with the staircase.

The first time I watched this, last spring, I was inspired to create a time-lapse video; but without preparing ahead of time I ended up standing up against a wall for an hour, taking pictures every minute, and then later writing a Python script to assemble the frames into an animated GIF. The results can be found here, and the technical details are here.

For the subsequent Summer Solstice I was ready with both an iPhone set to time-lapse mode and a Raspberry Pi programmed to take pictures every 5 seconds. The result from the Raspberry Pi is now on YouTube (watch the stripes of sunlight on the top stairs, not the people):

Technical details of how the Raspberry Pi was configured may be shared later. Instead of trying to assemble the time-lapse video on the Raspberry Pi itself, this video was assembled using iMovie on an iMac.   (I tried to use software called TLDF, but it requires frame sizes of at least 800 pixels, and the frames captured for this video were 640×480.) The result was an mp4 video file instead of an animated GIF. Perhaps I’ll get to try TLDF at the fall equinox….