by a Thinker, Sailor, Blogger, Irreverent Guy from Madras

Earth picture from Cassini and MESSENGER

Wow!  NASA has released the images of Earth and Moon taken by their Cassini spacecraft orbiting the planet Saturn and one take by their MESSENGER spacecraft buzzing the planet Mercury, on the same day - 19th July 2013.

In the Cassini image, our planet Earth and Moon are visible through a gap in the rings of Saturn.  The wide-angle camera on board the Cassini is an impressive 1.44 billion kilometres from Earth.

The 3rd rock from the Sun appears as a blue dot at centre right; the Moon can be seen as a fainter protrusion off its right side. An arrow indicates their location.

In the MESSENGER image, Earth and the moon appear as a pair of bright star-like from a distance of 98 million kilometres from Earth.  The wide-angle camera of the Mercury Dual Imaging System takes Black and White pictures, while the Cassini’s is in colour.

NASA explains that the Earth and the moon appear very large in the MESSENGER picture because they are overexposed. Because MESSENGER is hunting for potentially dim satellites (of Mercury), long exposures are required to capture as much light as possible. Consequently, bright objects in the field of view become saturated and appear artificially large.

In contrast the Cassini cameras had a different problem to solve.  Pictures of Earth from the outer solar system are rare because from that distance, Earth appears very close to the Sun.

Just like a human’s eye, a camera's sensitive detectors can be damaged by looking directly at the sun. Cassini took this image when the sun had temporarily moved behind Saturn from the spacecraft's point of view and most of the light was blocked - sort of shot this picture from the shadow of Saturn.


(cropped from original image courtesy NASA/JPL-Caltech/Space Science Inst.)

My Childish half chortles, ‘Look at the picture of Saturn.  Sure does not look anything like in Flash Gordon adventures! Except for the arrow, that is!’


Read more about them (Cassini and MESSENGER, not Flash Gordon) at NASA-JPL.


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