Бледная голубая точка: Фотография Земли от Voyager 1

the photograph
Photograph of Earth by Voyager 1

Pale Blue Dot is a photograph of Earth taken on February 14, 1990, by the Voyager 1 space probe from an unprecedented distance of approximately 6 billion kilometers (3.7 billion miles, 40.5 AU), as part of that day's Family Portrait series of images of the Solar System. In the photograph, Earth's apparent size is less than a pixel; the planet appears as a tiny dot against the vastness of space, among bands of sunlight reflected by the camera. Commissioned by NASA and resulting from the advocacy of astronomer and author Carl Sagan, the photograph was interpreted in Sagan's 1994 book, Pale Blue Dot, as representing humanity's minuscule and ephemeral place amidst the cosmos. Over the years, the photograph has been revisited and celebrated on multiple occasions, with NASA acknowledging its anniversaries and presenting updated versions, enhancing its clarity and detail.

In September 1977, NASA launched Voyager 1, a robotic spacecraft on a mission to study the outer Solar System and eventually interstellar space. After the encounter with the Jovian system in 1979 and the Saturnian system in 1980, the primary mission was declared complete in November of the same year. Voyager 1 was the first space probe to provide detailed images of the two largest planets and their major moons. The spacecraft, still travelling at , is the most distant human made object from Earth and the first one to leave the Solar System. Voyager 1 was expected to work only through the Saturn encounter. When the spacecraft passed the planet in 1980, Sagan proposed the idea of the space probe taking one last picture of Earth. He acknowledged that such a picture would not have had much scientific value, as the Earth would appear too small for Voyagers cameras to make out any detail, but it would be meaningful as a perspective on humanity's place in the universe. A proposal to continue to photograph Earth as it orbited the Sun was rejected.

Voyager 1s Imaging Science Subsystem (ISS) consists of two cameras: a 200 mm focal length, low resolution wide angle camera (WA), used for spatially extended imaging, and a 1500 mm high resolution narrow angle camera (NA) – the one that took Pale Blue Dot – intended for detailed imaging of specific targets. Both cameras are of the slow scan vidicon tube type and were fitted with eight colored filters, mounted on a filter wheel placed in front of the tube. The challenge was that, as the mission progressed, the objects to be photographed would increasingly be farther away and would appear fainter, requiring longer exposures and slewing (panning) of the cameras to achieve acceptable quality. The telecommunication capability also diminished with distance, limiting the number of data modes that could be used by the imaging system. After taking the Family Portrait series of images, which included Pale Blue Dot, NASA mission managers commanded Voyager 1 to power its cameras down, as the spacecraft was not going to fly near anything else of significance for the rest of its mission, while other instruments that were still collecting data needed power for the long journey to interstellar space.

The design of the command sequence to be relayed to the spacecraft and the calculations for each photograph's exposure time were developed by space scientists Candy Hansen of NASA's Jet Propulsion Laboratory and Carolyn Porco of the University of Arizona. At that time, the distance between the spacecraft and Earth was 40.47 astronomical units (6,055 million kilometers, 3,762 million miles). The data from the camera was stored initially in an on board tape recorder. Transmission to Earth was also delayed by the Magellan and Galileo missions being given priority use of the Deep Space Network. Then, between March and May 1990, Voyager 1 returned 60 frames back to Earth, with the radio signal travelling at the speed of light for nearly five and a half hours to cover the distance. Of the 640,000 individual pixels that compose each frame, Earth takes up less than one (0.12 of a pixel, according to NASA). The light bands across the photograph are an artifact, the result of sunlight reflecting off parts of the camera and its sunshade, due to the relative proximity between the Sun and the Earth. Voyager's point of view was approximately 32° above the ecliptic. Detailed analysis suggested that the camera also detected the Moon, although it is too faint to be visible without special processing.) Earth is a pale blue dot, rather than dark blue, because white light reflected by clouds combines with the scattered blue light. Rayleigh scattering, which causes Earth's blueness, is enhanced in an atmosphere that does not substantially absorb visible light, unlike, for example, the orange brown color of Titan, where organic haze particles absorb strongly at blue visible wavelengths. Earth's plentiful atmospheric oxygen, which is produced by photosynthetic life forms, oxidizes organics in the atmosphere and converts them to water and carbon dioxide, causing the atmosphere to be transparent to visible light and allowing for substantial Rayleigh scattering and hence stronger reflectance of blue light.|title=|source=

In 2015, NASA acknowledged the 25th anniversary of the photograph. Ed Stone, Voyager project scientist, commented: "Twenty five years ago, Voyager 1 looked back toward Earth and saw a "pale blue dot", an image that continues to inspire wonderment about the spot we call home." In 2020, for the image's 30th anniversary, NASA published a new version of the original Voyager photo: Pale Blue Dot Revisited, obtained using modern image processing techniques "while attempting to respect the original data and intent of those who planned the images." Brightness levels and colors were rebalanced to enhance the area containing the Earth, and the image was enlarged, appearing brighter and less grainy than the original. The direction of the Sun is toward the bottom, where the image is brightest. To celebrate the same occasion, the Carl Sagan Institute released a video with several noted astronomers reciting Sagan's "Pale Blue Dot" speech.