[ Watch the Video: Moon’s Dark Side Doesn’t Exist ]
Brett Smith for redOrbit.com – Your Universe Online
A newly released NASA video reminds us that there is no such thing as a dark side of the moon – just a far side.
Created from a patchwork of images taken by the Lunar Reconnaissance Orbiter (LRO), the video shows a 360-degree rotation of a fully-illuminated moon.
[ Watch the Video: Rotating Moon From LRO ]
“Let’s imagine that the sun is directly overhead the entire moon,” Petro explained. “For every point on the lunar surface, how bright would it be if the sun were directly overhead?”
The video is just one result of the four years the LRO has spent circling the moon. The images of the lunar surface used for the video were taken with the probe’s Wide Angle Camera (WAC), which has a very wide field-of-view. The field-of-view allowed NASA scientists to create a near-global topographic map of the Moon, 360 degrees of longitude and 80 degrees north to 80 degrees south of latitude.
The wide field-of-view also created challenges for patching together the images and recreating lunar colors. Because the various perspective changes from the center to the edges of each image’s frame, the perceived reflectance of the Moon shifts as the camera angle changes. In images captured by the WAC, the lunar surface looks most reflective in the center of the image. This effect causes in a pole-to-pole striped image when making an uncorrected image mosaic.
To fix this effect, scientists took 36 nearly complete global mosaics, comprised of 110,000 WAC images, and determined an equation that included Sun angle and view angle result with respect to reflectance changes. This equation was applied to each pixel in those 110,000 WAC images to adjust the measured brightness everywhere on the Moon.
All those calculations allowed for the creation of a crystal clear view of the so-called dark side of the moon. This side of the moon actually receives sunlight on a daily basis. However, because the moon’s rotation syncs perfectly with its orbit around the Earth – we never get to see the moon’s far side.
“The only way we can see the far side of the moon is with a spacecraft,” said Petro. “The important part of the video shows that there is no dark side of the moon — there’s a far side.”
Topographical variations on the moon are difficult to see in the video, but differences in albedo – relative reflectance – are enhanced. The moon’s craters only get limited sunlight and appear darker than the surrounding areas.
The LRO has been orbiting the moon since 2009, gathering terabytes of data on the lunar surface. In addition to creating the newly released mosaic video, the LRO mission has also created the most detailed topography map of the moon.
The LRO has also been used to test a new laser-based, deep-space communication system. In January, NASA successfully transmitted an image of the Mona Lisa from the Goddard Space Flight Center in Greenbelt, Md. to the LRO using the system.