‘Earthrise’ photographed from the moon

NASA has released a photo of Earth’s “rise” over the lunar horizon. The Lunar Reconnaissance Orbiter or LRO took the picture, or actually pictures. The LRO flew 134km above the Compton lunar crater while the photo was taken.

Taking a snapshot of the earth is no mean feat with the LRO. The spacecraft must first tilt on its side, in this case at an angle of 67 degrees; then the LRO must rotate in the flight direction to capture the lunar horizon as wide as possible on the sensitive plate with the vessel’s narrow-angle camera. All this while the device travels at 1600 meters per second or 5760 kilometers per hour relative to the lunar surface.

The Earth, seen from above the Compton Crater on the Moon. The Earth is at the center at 4.04°N, 12.44°W, just off the coast of Liberia. The photo sequence was started on October 12, 2015, 12:18:17.384 UTC Source: Arizona State University

The LRO’s high-resolution camera has a lens with a narrow angle of view and takes black and white photos. The camera with the wide-angle lens takes color photos. To process that data into an image, a lot had to be done, Arizona State University writes on its LRO Camera blog, which also contains high-resolution tiff files of the photos.

The black and white photo with the narrow-angle camera is taken only once. This photo has the high resolution. The wide-angle camera takes different photos. The pixel scale of the small-angle camera is 75 times smaller than that of the wide-angle. By using different wide-angle photos, a sharp color version of the plate can still be made. For each wide-angle pixel, the Earth had been photographed between twenty and fifty times. The lunar surface looks like it was taken with the narrow-angle camera. The colors are approximate, as the spectrum that the wide-angle camera detects is a combination of the 604nm, 556nm and 415nm bands, i.e. orange, yellow-green and violet. This has been converted to red, green, and blue for a display consistent with human perception.

Technically, the Earth will never “rise” when viewed from the Moon, because the Moon has a solid side to Earth. If the Earth is visible on the moon, it will remain visible.