If the midweek hump has you in a contemplative spirits, this stunning image of Earth as pictured by the Cassini spacecraft from Saturn, 898 million miles (1.44 billion kilometers) away, may offer a little context. The Earth and the Moon appear to be seemingly insignificant specks from the perspective of the spacecraft from its orbit around the gas giant, the second biggest planet in the Solar System. But as it turns out, Cassini is actually talking us up.
The image, taken on Friday, represents the first time that Cassini–Huygens (to give the spacecraft its full name) has captured the Earth and Moon as distinguishable from each other using its highest res wide-angle camera. Both the Earth and the moon actually appear larger than they should due to the long exposure used to capture as much light as possible. At the distance of Cassini from Earth, a single pixel of the wide-angle camera captures a distance of 53,800 miles (86,600 km) across, whereas the diameter of Earth is only about 7,900 miles (12,700 km). If a single flashlight could emit as much light as the Earth reflects, it would look just the same to Cassini if you pointed it in its direction.
This was a rare opportunity to capture such an image. Normally, the Earth's proximity to the Sun rules out such pictures being taken, as the Sun puts the extremely sensitive sensors of such cameras at risk. But in this case, the Sun had moved behind Saturn from Cassini's point of view, hence Saturn itself appearing as a dark mass to the left of the image. This is only the third image of Earth captured from the outer solar system where the gas giants reside.
NASA also says that this is the first time that people on Earth had advance warning that a photo of the planet was to be taken from interplanetary range. At NASA'S invitation, 20,000 people around the world are thought to have photographed themselves smiling and waving at Saturn to coincide with the event.
"We can't 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 Cassini project scientist Linda Spilker. "Cassini's picture reminds us how tiny our home planet is in the vastness of space, and also testifies to the ingenuity of the citizens of this tiny planet to send a robotic spacecraft so far away from home to study Saturn and take a look-back photo of Earth."
The image will form part of a mosaic of Saturn's rings which NASA scientists are currently piecing together. This is set to be released some time in the coming weeks.
The image was joined by another of planet Earth taken on the same day by the MESSENGER spacecraft from a distance of 61 million miles (98 million kilometers) from its orbit about Mercury.
Launched in 1997, Cassini arrived at Saturn in 2004, commencing its 4-year mission to study the planet, its rings, and its natural satellites. Its second mission, Cassini Equinox, extended its observation of the Saturn system by 2 years. Its third and current mission, Cassini Solstice, will run until 2017, allowing observation of a complete seasonal cycle on the planet since its arrival. The mission will come to an end with a series of close flybys of the planet passing inside its rings. Cassini will be destroyed shortly after when it plummets into Saturn itself.
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