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Time-lapse movies are compelling because they give us a glimpse of events that are continually occurring around us, but at a rate normally far too slow to for us to observe directly. A History of the Sky enables the viewer to appreciate the rhythms of weather, the lengthening and shortening of days, and other atmospheric events on an immediate aesthetic level: the clouds, fog, wind, and rain form a rich visual texture, and sunrises and sunsets cascade across the screen.
This is a work in progress. Currently, an image of the sky is being captured every 10 seconds from a camera installed on the roof of the Exploratorium, on the edge of San Francisco Bay. The images collected over each 24-hour period are assembled into a 6 minute movie (at 24 frames/second).
The final piece will consist of a large projected grid of 365 movies, each representing one day of the year, and cycling in parallel through consecutive 24-hour periods. The viewer can stand back and observe the atmospheric phenomena of an entire year in just a few minutes, or approach the piece to focus on a particular day.
This will also be an active piece. The camera will continue to collect images and integrate them with the montage daily. The visualization will therefore vary from day to day, and will always display the most recent 365 days.
Events and Exhbitions
Here is the latest full-year version of "A History of the Sky" (I suggest watching it in full-screen HD mode):
This is an earlier movie made from images from the camera's first 42 days on the roof of the Exploratorium. The earliest day is in the upper left, and consecutive days follow left to right, then down, with the most recent day in the lower right. It starts a little before sunrise, so it's dark for the first few seconds:
Keep in mind that all of the days are synchronized, so at any given moment, you're looking at the sky at the exact same time of day for each of the panels. The cascading effect at sunrise and sunset is caused by the variations in day length.
Here is a more recent movie, showing 126 days, with some titles and music thrown in (I encourage you to click through to YouTube and watch it in full screen at 720p):
I envision this as a large projected piece, as illustrated at the top of thie page. However there are many possible approaches, and the site of installation could be a consideration. For example, the images could be arranged circularly, which would play interestingly with the year's cyclical nature. Here is another illustration of how the piece might be displayed:
The Camera Rig
The rig consists of an old four-megapixel compact digital camera controlled by a small, low-power computer. I looked into some of the "netcams" that are available, but even the pricey ones had unimpressive image quality. On the other hand, my old Canon A520 takes pretty nice pictures.
I'm trying to capture as much of the sky as possible, so I attached a wide-angle conversion lens, which fits over the existing optics.
The computer is a Soekris net4801, on which I've installed Ubuntu Linux. The hardware is intended for use as a general-purpose networking computer, but it works perfectly for this job, as it has a USB port, and ethernet ports (remote access is a requirement). This system has 4GB of Compact Flash storage, enough for several days' images. The software controlling the camera is gPhoto, an open-source image capture application.
This all fits inside of a NEMA Type 3 enclosure, which I salvaged from a junk yard.
The enclosure is mounted so that the optical axis of the camera points 45 degrees above the horizon. One important factor is that the sun never enter the frame. This would complicate exposure issues, and I think the piece works best with just sky, clouds, and fog. To accomplish this, the camera is faced due north. Even with the wide-angle lens, the sun will always be just out of view.
If you're interested in building your own system, check out my how-to article, "Slow Down To Speed Up" in issue 21 of Make Magazine.
Images from the camera computer are are continually downloaded over the network to another system, sitting safely inside the building: a desktop PC running Linux, with a one-terabyte external RAID disk array.
Maintaining uptime is important for this project. The camera computer and the camera itself run off an uninterruptable power supply. If the network is tempoarily interrupted, the camera computer can continue to store image files locally until connectivity is restored, and the downloads to the storage system can resume.
I also built a simple relay circuit to power cycle the camera if it gets in a bad state, which can be controlled by software (relay circuit is on the right):
Processing the Images
The job of assembling the images into a movie is done on the main storage system. The process is currently a manual one, but will be automated in the future to produce a new movie every day, based on the prior 365 days' images. The process includes: