Ever since NASA's Lunar Reconnaissance Orbiter began circling the Moon at low altitude in mid-2009, planetary scientists and the public have marveled at the incredible trove of observations it's been beaming back to Earth. Most often in the spotlight are the jaw-dropping closeups of Apollo landing sites by the Lunar Reconnaissance Orbiter Camera (LROC). It can resolve the surface at 2 feet (0.5 m) per pixel — good enough to reveal even the paths worn in the lunar soil by the astronauts' boots.The work of LROC's wide-angle camera, which provides surface context for those incredible narrow-angle shots, has largely gone unheralded … until now. This past week the team released a new mosaic of the Moon's near side taken entirely with wide-angle frames. Acquired during a two-week period in December, the 1,300 black-and-white frames create a full-disk mosaic measuring 24,000 pixels across. Gulp!
"As the Moon rotated under LRO's orbit," explains LROC team leader Mark Robinson (Arizona State University), "the ground track progressed from east to west (right to left in this mosaic)." The image run was timed to keep the Sun high up in the lunar sky but not straight overhead (its altitude varied from 69° to 82°). This created enough shadowing to define crater rims and other topography crisply, unlike the shadow-free view that we see during a full Moon. The combined image shows slight banding where the 1,024-pixel-wide swaths were stitched together.Weighing in at just 2 pounds (0.9 kg), LROC's wide-angle camera is small enough to fit in your hand. It features an aperture only 1.2 mm across and a focal length of just 6 mm (for visible-light work). Yet from LRO's very low orbit, currently only 20 miles (30 km) up, this mighty mite can pick out surface details as small as 250 feet (75 m). Click here to view the specifications for LROC's wide- and narrow-angle cameras.
The image looks dark because Robinson and his team have kept the Moon as it really is: dark. On average, the lunar surface reflects only about 12% of the sunlight that strikes it. So a full Moon really isn't dazzlingly bright — it only looks that way to our eyes because of the contrast with the black sky around it.
If your computer's up to it, you can download the full half-gigabyte mosaic here.