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NASA spacecraft snaps view of Earthrise from the moon
BY STEPHEN CLARK
ASTRONOMY NOW

Posted: May 11, 2014


Earlier this year, NASA's Lunar Reconnaissance Orbiter turned away from the moon and recorded an image of Earth looming above the lunar horizon, a modern version of the iconic "Earthrise" photograph taken by the Apollo 8 astronauts 45 years ago.


This image, captured Feb. 1, 2014, shows a colorized view of Earth from the moon-based perspective of NASA's Lunar Reconnaissance Orbiter. Credit: NASA/Goddard/Arizona State University
 
The image was taken Feb. 1 by LRO's wide angle camera developed by scientists at Arizona State University in Tempe. The wide angle imager is one of three cameras on LRO, which arrived at the moon in June 2009 and is now in an extended mission.

The orbiter's wide angle camera did not take the picture the way Apollo astronauts snapped photos of Earth when they visited the moon more than 40 years ago.

Mark Robinson, the lead scientist for LRO's camera suite, described what makes the orbiter's camera different:

"The LROC Wide Angle Camera (WAC) is very different than most digital cameras. Typically resolution is reported as the number pixels in a single image, a cell phone camera today has more than 5 million pixels (5 megapixels). A single WAC frame has only 9856 pixels, however the WAC builds up a much larger image by exposing a series of images (or frames) as LRO progresses in its orbit; this type of imaging is called 'push-frame.'"


In the animation, the "venetian blind" banding demonstrates how a WAC image is built up frame-by-frame. The gaps between the frames are due to the real separation of the WAC filters on the CCD. The longest wavelength (689 nm) band is at the bottom of the scene, and the shortest (415 nm) is at the top; note how Earth is brighter when it enters the top band due to the blue from the ocean. The frames were acquired at two second intervals, so the total time to collect the sequence was five minutes. The video is about 20 times faster than reality. See a larger version. Credit: NASA/Goddard/Arizona State University
 
The wide angle camera builds up a collection of image strips to cover the entire globe once a month, according to scientists.

The Earthrise image released last week is a color composite using data from the camera's seven color bands in visible wavelengths. The moon is a greyscale composite, while the color of Earth was composed from three of the camera's color bands representing blue, green and red.

"These wavelengths were picked as they match well the response of the human eye, so the colors are very close to true, that is what the average person might see," Robinson wrote in a post on an Arizona State University website. "Also, in this image the relative brightness between the Earth and the moon is correct, note how much brighter the Earth is relative to the moon."

Japan's Kaguya spacecraft beamed high-definition imagery of Earthrise back to Earth during its mission in 2007 and 2008, providing another spectacular retake on the classic photographs taken by the Apollo astronauts. Credit: JAXA
 

Follow Stephen Clark on Twitter: @StephenClark1.

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