Sundials - World's Oldest Clocks

North American Sundial Society

Kevin Murphy, artist and photographer, set up a time-lapse camera on the roof of the San Francisco Exploratorium to record the sky every 10 seconds, 24 hours per day for an entire year. The camera points due north at and elevation of 45 degrees, which means that you won’t see any dramatic sunrise or sunset, nor will you see a burning image of the sun. Even with the wide-angle lens, the sun is always kept just out of view. But what a wonderful view of the sky: Look closely at the video and you’ll see moving clouds, fog, rain, and differing colors of the sky.

Most stunning is the changing length of the day. Summer morning twilight begins about 4:10am (Pacific Standard Time) and evening twilight ends about 8:10pm, but you must be patient for the winter sky to appear. Winter morning twilight begins about 6:50am (PST) and evening twilight ends about 5:30pm. (There’s a small running clock in the bottom right corner to chart your progress). You’ll see the dramatic difference between summer and winter with days in darkness patiently waiting their turn at sunrise and conversely, the fast quenching of the blue sky into darkness well before the summer frames show any sign of paling.

Each frame is digitally photographed at 1024x768 pixels, that with compression, requires about half a terabyte storage per year. Kevin Murphy has been creative with the sky display: Thumbnail videos of each day of the year are collectively represented in a tiled mosaic 20 days wide by 18 days tall, showing 360 days of sky all at once. The images are arranged chronologically, and are synchronized by time of day, beginning before summer sunrise. Time is compressed in playback at 24 frames/second so that each second represents 4 minutes of time.

This is still a work still in progress: As the camera on the Exploratorium roof continues to collect images of the sky, they will be integrated into the daily montage. Therefore the video will vary from day to day, always displaying the most recent 365 days.

Visit http://www.murphlab.com/hsky/ for more information. Below is his video. It’s best played in full-screen HD resolution. Click the middle arrow to start, then click the bottom right frame box.