The Sciences

An Alien's-Eye View of Earth

Out There iconOut ThereBy Corey S PowellJul 26, 2013 8:08 AM

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Earlier this week, the visionaries who operate NASA's Cassini spacecraft released a remarkable snapshot of Earth as seen from Saturn. It got a ton of media attention, and rightly so. It is a stunning celestial view that no human being can see first-hand, but that billions of people around the world can now experience vicariously. It starkly illustrates how small we are within the universe, while simultaneously celebrating the grand things our little species is capable of. I went on cable news to talk about it, and DISCOVER blogger Tom Yulsman wrote a poignant post about it. But that new Cassini image is far from the only perspective-busting picture that has come in from humanity's space fleet. In fact, there is a whole portfolio, many of them rarely seen. Collectively they offer what I call an alien's-eye view of Earth: They show what our planet might look like to extraterrestrial scientist scoping out our planet from afar. Here I've pulled together a few of my favorites. [To follow me on Twitter: @coreyspowell]Earthset on the moon. The Apollo astronauts captured shots of Earth rising on the moon, but this is the only full sequence I know of that shows Earth setting. (Both events occur only from orbit around the moon or from some other mobile vantage. For a stationary observer on the lunar surface, Earth hangs nearly motionless in the sky.) In 2007 Japan's Kaguya spacecraft--also known as Selene--took both still images and HD video of Earth ominously vanishing from view. Earth's south pole is facing up; Australia is at upper left on the globe but turned upside-down because of the orientation. The whole sequence covers about 70 seconds. (Credit: JAXA/NHK)

Solar eclipse from space. A solar eclipse happens when the moon passes in front of the sun...from Earth's perspective. From the moon's perspective, seen here, the moon's shadow sweeps across the face of the Earth, giving our planet something of a black eye. The whole process lasts just a few hours and is difficult to capture, but NASA's Lunar Reconnaissance Orbiter managed the feat on May 20, 2012. The center of the moon's shadow lies off the coast of Alaska in this annotated image. The shadow itself looks gray and soft because the moon was too far away at the time to completely cover the sun, so some sunlight leaked into the darkened area. (Credit: NASA/GSFC/Arizona State University)

Crescent Earth: daylight and night lights. There are at least three very cool things going on in this image. First, it shows Earth as a slender crescent, highlighting the thin layer of atmosphere and the blue of the ocean that mark ours as a habitable planet. Second, the image also picks up a key trait that marks Earth as an inhabited planet: the lights of cities at night. Look carefully and you can see a bright line that marks the location of the Nile valley. (Capturing both sunlight and artificial light required a double exposure, with the two snaps taken 20 minutes apart.) Third, this view comes from the European Space Agency's Rosetta spacecraft, which used Earth's gravity to steer it toward Comet Churyumov–Gerasimenko. In November, 2014, if all goes well Rosetta will deploy a lander and make the most detailed study ever of a comet. (Credit: ESA/MPS/OSIRIS)

Earth and the moon from below. Our quaint notions of up and down mean nothing in space, as illustrated by this family portrait taken by the NEAR spacecraft in 1998 while it was en route to the near-Earth asteroid Eros. From a distance of 400,000 kilometers, the camera is looking up (or is it down?) at Earth's south pole, offering a view unavailable from any planet or moon in the solar system. Antarctica sits right in the middle. A video of the flyby makes the geometry much clearer. Sharp-eyed readers will notice that this picture has been doctored for dramatic effect: The moon has been brightened by a factor of 5 (in reality it is as gray as asphalt), and the distance between Earth and moon has been greatly cropped. That explains why the shadows of the two do not line up properly. (Credit: JHU/APL)

The solar system, inside out. The same day that the Cassini spacecraft was peering inward toward Earth from Saturn, the MESSENGER spacecraft was gazing outward from Mercury. Saturn has beautiful rings; Mercury looks a lot like the moon and has a terrible PR problem. So while everyone was celebrating the Saturn image, this similarly fascinating shot got little attention. Well, here it is in all its glory. Like many extreme perspective shots, it doesn't have its full impact until you parse exactly what you are looking at. The big frame (below left) shows a panorama of the whole solar system laid out in the sky as seen from the world closest to the sun. Callouts identify the planets; the background frames also pick up a little bit of the Milky Way in the sky. The inset (below right) zooms in on Earth and the moon. To an astronaut staring up into the airless night sky of Mercury, Earth would be a brilliant blue dot, outshining any star, while the moon would appear as a second-magnitude companion dot half a degree away. All the hopes, dreams, fears, hates, and loves of the world cling to that single blip of light. It reminds me of Neil Armstrong's impression when he looked up from the surface of the moon: "It suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn't feel like a giant. I felt very, very small." (Credit: NASA/JHUAPL/CIW).

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