Astronomy hobbyist Peter Rosén couldn’t afford to launch a space probe, but he did have a telescope, a camera, a laptop and a dream to recreate Voyager 1’s flyby footage of Jupiter and its swirling cloud belts. He wasn’t sure exactly how he'd do it—still, his final opportunity for the next twelve years was coming up: Winter of 2013 would be prime time for Rosén, in Sweden, and other astronomers in the Northern Hemisphere to catch a glimpse of the gas giant in the sky.
His project, entitled Voyager 3, had a challenge from the outset: to create a full timelapse, Rosén would need hundreds of photographs taken consistently throughout several months to construct maps of the planet’s surface which would add up to one timelapse video (above).
Explains Rosén, Jupiter is special to amateur astronomers because “it is an ever-changing planet." The fastest-spinning planet in our solar system, Jupiter rotates in less than 10 hours; its movement is visible in photos even two minutes apart. On the off-chance he was faced with a cloudy sky, an astronomer in a different location might have better luck. So he did what any enterprising DIY-er would do: he proposed the idea on a local astronomy forum and formed a super team of seven likeminded stargazers.
For each team member, the instructions were simple: take a single photo every hour for as long as possible—typically four to five hours per night—and to continue from the point they left off the following day to capture one whole rotation of Jupiter’s surface. Explains Rosén, to take photos of planets, one must use highly sensitive video cameras. In reality, one photo of the planet is created from hundreds—even thousands—of layered images. Their cameras captured around two minutes of footage, roughly 600-2000 frames. Using an astronomical image processing software, the frames were then stacked to create high-resolution color photos which were sent to Rosén, a.k.a. “the center of operation.”
As Rosén received photos from team members, he re-edited them so that they were homogenous. He then sent his edits to colleague Martin Högberg, who used a program called WinJupos to stitch the photos into cylindrical and polar projections of Jupiter’s surface. But as Rosén pieced together the team's projections, he realized essential pieces of information—specifically the map's edges—were missing, and that the ends of his map couldn’t be connected. To tackle this problem, he stretched the material he had, using every pixel at his disposal to fill in the gap. Thus, by end of December, the first man-made “map” of Jupiter’s surface was realized.
Although January and February’s weather took a turn for the worse, the crew pushed ahead and by March, they had successfully created 18 maps of Jupiter’s surface. Because the maps were not consistent in timing—some were as many as 12 days apart—the resulting animation was far from smooth. To solve this, Rosén used morphing techniques to generate frames that would fill in the gaps in the timeline, stretching 18 images into one image per each of the 90 days. This successful solution gave Rosén and company the footage for their epic flyby timelapse.
“True, the first animation of Jupiter’s cloudbelts was shot by NASA 35 years ago. But since then nobody has attempted to recreate it,” says Rosén. “I wanted to see if it was possible. And it was.”
So, what's next for Rosén and company? For one thing, the DIY astronomer plans to choreograph a ballet of Jupiter’s 67 moons. Sounds easy, right? With a team like Voyager 3, anything seems possible.
For more detail on how to shoot a timelapse of Jupiter, check out Rosén’s blog post