The Blue Marble

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Original caption: "View of the Earth as seen by the Apollo 17 crew traveling toward the moon. This translunar coast photograph extends from the Mediterranean Sea area to the Antarctica south polar ice cap. This is the first time the Apollo trajectory made it possible to photograph the south polar ice cap. Note the heavy cloud cover in the Southern Hemisphere. Almost the entire coastline of Africa is clearly visible. The Arabian Peninsula can be seen at the northeastern edge of Africa. The large island off the coast of Africa is Madagascar. The Asian mainland is on the horizon toward the northeast."

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 29,000 kilometres (18,000 mi).^[1]

The name also has 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.

[edit] The photograph

The snapshot taken by astronauts on December 7, 1972, 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).

[edit] History

The photograph was originally taken "upside down" in that the South Pole was at the top of the photograph. This is because of the orientation in which the astronauts were traveling at the time. ^[3][4]

The photograph was taken on December 7, 1972, at 5:39 a.m. EST (10:39 UTC), about 5 hours and 6 minutes after launch^[5], and about 1 hour 54 minutes after the spacecraft left 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 also was illuminated.

The photograph's official designation is AS17-148-22727. (The photograph AS17-148-22726, taken just before and nearly identical to 22727, also is used as a full-Earth image.) The photographer used a 70-millimeter Hasselblad camera with an 80-millimeter lens.^[6] 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. After the mission, evidence showed that although the photograph could have been taken by any of the astronauts, Jack Schmitt probably took the famous image,^[2] although the official photographer still cannot be verified completely ^[7].

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 of an illuminated face of 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 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 upside down from the usual view of North at the top, but was rotated before it was distributed.^[3][4]

[edit] The satellite imaging series

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.^[8] At the time, 1km/pixel this was the most detailed imagery available free, and permitted reuse^[9] 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. 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).^[10] 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 also have been released, among them a music visualization for the PS3 that is based on the texture data.^[11][12]

[edit] Other applications of the term blue marble

Subsequent similar images of Earth (including composites at much higher resolution) also have been termed "blue marble" images, and the phrase "blue marble" (as well as the picture itself) is used - such as in the Earth flag - frequently by environmental activism organisations or companies attempting to promote an environmentally conscious image. There also has been a children's television program called Big Blue Marble.

Blue Marble composite images generated by NASA in 2001 (left) and 2002 (right).

[edit] See also

• Deep Space Climate Observatory, an as-yet-unlaunched satellite which would have regularly produced full Earth images
• Earthrise, another iconic picture of the Earth taken aboard Apollo 8
• Pale Blue Dot, an image of the Earth taken by Voyager 1
• Stewart Brand, author who in 1966 lobbied NASA to release a then-rumored satellite photograph of the entire Earth
• Whole Earth Catalog, an eclectic catalog compiled by Brand which was inspired in part by photographs of the Earth as a globe
• Earth flag, a flag featuring the Blue Marble photo

[edit] References

[edit] External links

• NASA history of Blue Marble image releases

[edit] 1972 photograph

• The one, the only, photograph of Earth a short list of places in which the image has been used.
• Apollo Image Atlas Photos from magazine NN of the 70mm Hasselblad camera used on Apollo 17 (includes the Blue Marble photo and others quite similar to it)

[edit] 21st century NASA composite images

• Blue Marble (2002)
  • Blue Marble Mapserver Web interface for viewing small sections of the above
• Blue Marble: Next Generation (2005; one picture per month)
  • Blue Marble Navigator Web interface for viewing local sections of the above, incl. links to other such interfaces, download sites etc.
  • Blue Marble: Next Generation in NASA World Wind