26 August 2013

Earth and Moon photographed from 900 million miles away, from the shadow of Saturn

For only the third time ever, Earth has been photographed from the outer Solar System. At a distance of 898 million miles, as seen by NASA’s Saturn-orbiting Cassini satellite, the Earth is a tiny, almost luminescent blue marble — or, perhaps, a not-quite-so-pale blue dot. If you zoom in (image below), you can even see the pale speck of the Moon next to Earth. As luck would have it, at almost exactly the same time, NASA’s MESSENGER satellite also captured an image of the Earth and Moon — this time from the inner Solar System, orbiting around Mercury (image below).

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The complete photo above is a mosaic of 33 different images captured over 15 minutes on Friday afternoon, July 19. In almost ten years of orbiting Saturn, Cassini has only had the opportunity to image Earth twice — and this time, in a cute bit of public relations, NASA actually issued a press release asking the denizens of Earth to smile and wave while the photo was being captured. In short, if you waved at around 16:30 EST on July 19, there’s a chance that Cassini captured some photons bouncing off your arm — or, to put it another way, if Cassini was equipped with a gazillionjiggerpixel sensor, you’d be able to zoom in and resolve your smiling face.

So you have some idea of the scale, at this distance (753,000 miles from Saturn, 898 million miles from Earth), each pixel of the image represents 43 miles on Saturn, and 53,820 miles on Earth (i.e. the Earth is just a single pixel, with reflected light and overexposure creating a halo around it). While creating the huge mosaic with its wide-angle camera, Cassini also took a narrow-angle photo that clearly shows the Earth and its Moon, which you can see below. The reason that Cassini has only managed to capture Earth twice is that it must be on the dark side of Saturn (so that the Sun doesn’t blow out the image), and Earth must be in the right position among Saturn’s bright and occluding rings. Every other bright object in the photo is a star.
In other news, NASA’s Mercury-orbiting MESSENGER also captured a photo of the Earth and Moon on the morning of July 19. As you can see in the image below, when there isn’t a huge planet or some beautiful rings in the foreground, the wide black expanse of space isn’t all that exciting. This photo, which was captured while MESSENGER continues its search for any moons orbiting Mercury, was taken at a distance of 61 million miles (98 million km) from Earth.

Over the last few years, Cassini has produced some of NASA’s most beautiful imagery of the universe. The Rose of Saturn depicted a hurricane on Saturn that’s twice the diameter of Earth. In 2011, Cassini managed to capture some perfect photos of Saturn and its moons Titan, Dione, and Tethys. And, of course, back in 2006 it took the first high-resolution deep-space photo of Earth, as seen from the shadow of Saturn (below).

Earth can be seen at the 10 o’clock position, inside the penultimate ring (click to zoom in)

Now read: 9 gigapixels, 84 million stars: Peer into the world’s most detailed photo of the Milky Way


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