Looking Up – Bob Eklund

Earth from SaturnOur home planet and its Moon appear as a mere dots—the Earth a pale blue and the Moon a stark white—in new color images taken from nearly 900 million miles away by the cameras on NASA’s Cassini spacecraft.  The images were taken on July 19, 2013, during an event that was observed and celebrated worldwide.

The July 19 Earth-imaging event marked the first time Earthlings had advance notice that their portrait was being taken from interplanetary distances.  It was the also the first time Cassini’s highest resolution camera captured the Earth and its Moon as two distinct objects.  NASA invited the public to acknowledge the occasion by either finding Saturn in their part of the sky and waving, or simply smiling and celebrating.  At least 20,000 people around the world participated.

“We may not be able to see individual continents or people in this portrait of Earth, but this pale blue dot is a succinct summary of who we were on July 19,” said Linda Spilker, Cassini project scientist, based at NASA’s Jet Propulsion Laboratory.  “Cassini’s picture reminds us how tiny our home planet is in the vastness of space, but also testifies to the ingenuity of the citizens of this tiny planet to be able to send a robotic spacecraft so far away from home to take a picture of Earth and study a distant world like Saturn.”

Pictures of Earth from the outer solar system are rare because, from that distance, Earth is very close to the bright Sun.  Just as a human being can damage his or her retina by looking directly at the Sun, a camera’s sensitive detectors can be damaged by looking directly at the Sun.  Cassini was able to take these images because the Sun had moved behind the planet Saturn from the spacecraft’s point of view, blocking out most of the light.

The Earth and the Moon can be seen in both narrow-angle and wide-angle images.  In both cases, the illuminated portions are smaller than the smallest resolvable objects the cameras can see from the distance of Saturn.

At the time of this picture, the Earth and Moon shone through a gap between the thin G ring, just outside Saturn’s main rings, and the brightest portion of the diffuse E ring created from the spray of geysers from the moon Enceladus.

“It thrills me to no end that people all over the world took a break from their normal activities to go outside and celebrate the interplanetary salute between robot and maker that these images represent,” said Carolyn Porco, the Cassini imaging team lead, based at the Space Science Institute, Boulder, Colo.  “The whole event underscores for me our ‘coming of age’ as planetary explorers.”

The wide-angle image is part of a larger mosaic—or multi-image portrait—that imaging scientists are putting together of the entire Saturn system.  The lighting conditions allow for special views of faint, dusty rings that are usually difficult to see from other angles or from ground-based telescopes on Earth.  It will likely take another several weeks for the full mosaic to be completed.

Cassini’s image carries on a NASA legacy of images of our fragile home from space, including the 1968 “Earthrise” image taken by the Apollo 8 Moon mission from about 240,000 miles away and the 1990 “Pale Blue Dot” image taken by Voyager 1 from about 4 billion miles away.

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