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Pale Blue Dot is a photograph of Earth taken on February 14, 1990, by the Voyager 1 space probe from an unprecedented distance of over 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. Voyager 1 was launched on September 5, 1977, with the initial purpose of studying the outer Solar System. After fulfilling its primary mission and as it ventured out of the Solar System, the decision was made to turn its camera around and capture one last image of Earth emerged, in part due to Sagan's proposition. 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.

Voyager 1 is a 722-kilogram (1,592 lb) robotic spacecraft on a mission to study the outer Solar System and eventually interstellar space. When the spacecraft passed the planet in 1980, Sagan proposed the idea of the space probe taking one last picture of Earth.

Pale Blue Dot was taken with the narrow-angle camera, a 1500 mm f/8.5 catadioptric cassegrain telescope whose design was based on the 1973 Mariner mission. 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 three frames were then recombined to produce the image that became Pale Blue Dot. Pale Blue Dot, which was taken with the narrow-angle camera, was also published as part of a composite picture created from a wide-angle camera photograph showing the Sun and the region of space containing the Earth and Venus. The wide-angle image was inset with two narrow-angle pictures: Pale Blue Dot and a similar photograph of Venus.

Earth appears as a blue dot in the photograph primarily because of Rayleigh scattering of sunlight in its atmosphere. 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.

In his 1994 book, Pale Blue Dot, Carl Sagan comments on what he sees as the greater significance of the photograph, writing: To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we've ever known.

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." To celebrate the same occasion, the Carl Sagan Institute released a video with several noted astronomers reciting Sagan's "Pale Blue Dot" speech. Audio recording of Carl Sagan reading from Pale Blue Dot (US Library of Congress) Video produced for Pangea Day with Sagan reading from Pale Blue Dot Cassini's Pale Blue Dot – European Space Agency

Quick Facts

• 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.
• Pale Blue Dot, which was taken with the narrow-angle camera, was also published as part of a composite picture created from a wide-angle camera photograph showing the Sun and the region of space containing the Earth and Venus.
• 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.
• Video produced for Pangea Day with Sagan reading from Pale Blue Dot
• The wide-angle image was inset with two narrow-angle pictures: Pale Blue Dot and a similar photograph of Venus.

Source material: Wikipedia - "Pale Blue Dot". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.