With its incredible beauty, a time-lapse of Jupiter’s moons Europa and Io orbiting the gas giant has recently gone viral on the Internet. Because the time-lapse is so amazing, many users have claimed that it isn’t real.
While it’s important to be suspicious of photographs posted online, especially when fake images are circulated as real in exchange for clicks, we’re happy to report that the beautiful little movie is 100 % real. The fact check was also done by Snopes, which you can see here.
Kevin M.Gill is the creator of this incredible video. M.Gill is a NASA-JPL engineer who specializes in planetary image processing. He created this video by combining several photographs captured by the Cassini space probe during a visit to Jupiter in 2001. (Yes, none of these images or parts of the video were created with a computer.)
In the footage, Io and Europa can be seen circling Jupiter. One of the reasons for the video’s suspicion is that Io, which is closer to Jupiter, appears to orbit at a slower rate than Europa, which is further away. There is, however, a simple explanation for this.
Kevin M.Gill explains: “The motion isn’t wholly accurate as I made it to look prettier than it was correct. It’s meant to portray the motion visible from a spacecraft that’s moving at a velocity faster than the moons are orbiting. So, from a stationary perspective, Io would move faster than Europa.”
Because you’re looking at Europa from the perspective of a spacecraft traveling to the left, such as Cassini, it appears to be circling quicker than Io. Now that it is closer, Europa appears to be moving faster. This is a common illusion: objects appear to move slower as they get further away because they appear smaller and hence take longer to pass through our eyes.
Consider yourself on a freeway, looking across at the cars traveling in the opposite direction. A plane can be seen traveling in the same direction as the cars behind them. From your viewpoint, the autos look to be traveling faster than the plane, but they are not.
You can check out more of his work here.