The Blue Marble is a famous photograph of the Earth, taken on December 7, 1972, by the crew of the Apollo 17 spacecraft, at a distance of about 45,000 kilometres (28,000 mi).[1]
The name has also been applied by NASA to a modern series of image data sets covering the entire globe at relatively high resolution, created by carefully sifting through satellite-captured sequences taken over time, to eliminate as much cloud cover as possible from the collated set of images.
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The snapshot — taken by astronauts on December 7, 1972, at 5:39 a.m. EST (10:39 UTC) — is likely one of the most widely distributed photographic images in existence.[2] The image is one of the few to show a fully illuminated Earth, as the astronauts had the Sun behind them when they took the image. To the astronauts, Earth had the appearance of a glass marble, hence the name.
The photograph was taken about 5 hours and 6 minutes after launch of the Apollo 17 mission,[5] and about 1 hour 54 minutes after the spacecraft left its parking orbit around the Earth, to begin its trajectory to the Moon. The time of Apollo 17's launch, 12:33 a.m. EST, meant that Africa was in daylight during the early hours of the spacecraft's flight. With the December solstice approaching, Antarctica was also illuminated.
An Indian Ocean cyclone can be seen in the upper right quadrant of the image. This storm had brought flooding and high winds to Tamil Nadu state on December 5, two days before the photo was taken.[6]
The photograph's official NASA designation is AS17-148-22727. (The photograph AS17-148-22726, taken just before and nearly identical to 22727, is also used as a full-Earth image.) The photographer used a 70-millimetre Hasselblad camera with an 80-millimetre lens.[7] NASA officially credits the image to the entire Apollo 17 crew–Eugene Cernan, Ronald Evans and Jack Schmitt–all of whom took photographic images during the mission with the on-board Hasselblad. Although the identity of the specific photographer of the Blue Marble remains unverified,[8] evidence examined after the mission suggests that it was likely Jack Schmitt.[2]
Apollo 17 was the last manned lunar mission. No humans since have been at a range where taking a whole-Earth photograph, such as The Blue Marble, would be possible.
The Blue Marble was the first clear image taken of an illuminated face of the Earth. Released during a surge in environmental activism during the 1970s, the image was seen by many as a depiction of Earth's frailty, vulnerability, and isolation amid the vast expanse of space. NASA archivist Mike Gentry has speculated that The Blue Marble is the most widely distributed image in human history.[2]
The picture originally was taken with South at the top of the image, but was rotated before it was distributed.[3][4]
In 2002, NASA released an extensive set of satellite-captured imagery, including prepared images suitable for direct human viewing, as well as complete sets suitable for use in preparing further works.[9] At the time, 1 km/pixel was the most detailed imagery available for free, and permitted for reuse[10] without a need for extensive preparatory work to eliminate cloud cover and conceal missing data, or to parse specialized data formats. The data also included a similarly manually assembled cloud-cover and night-lights image sets, at lower resolutions.
The release was greeted enthusiastically, and a subsequent release was made in 2005, named Blue Marble Next Generation.[11] This time, it was produced with the aid of automated image-sifting, which enabled the inclusion of a complete, cloud-free globe 'frozen in time' for each month of the year, at even higher resolution (500m/pixel).[12] The original release of a single-image set covering the entire globe had, of necessity, not been a true reflection of the extent of seasonal snow-and-vegetative cover across both hemispheres, but this newer release closely modeled the changes of the seasons.
A number of interactive viewers for this data have also been released, among them a music visualization for the PS3 that is based on the texture data.[13][14]
Subsequent similar images of Earth (including composites at much higher resolution) have also been termed "blue marble" images, and the phrase "blue marble" (as well as the picture itself) is frequently used, as in the Earth flag by environmental activist organizations or companies attempting to promote an environmentally conscious image. There has also been a children's television program called Big Blue Marble.
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