Pale Blue Dot - Photograph

Photograph

The Pale Blue Dot was taken when the Voyager 1 spacecraft reached the edge of the solar system, 12 years after its launch and travelling at 40,000 miles per hour (64,000 km/h) at a record distance of about 6 billion kilometers. On February 14, 1990, having completed its primary mission, the spacecraft was commanded by NASA to turn around and photograph the planets of the solar system. 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 JPL and Carolyn Porco of the University of Arizona. The NASA imaging team photographed the outer planets first because they were worried that pointing the camera near the sun would blind the spacecraft's cameras and prevent more pictures from being taken. Between February 14, 1990 and June 6, 1990, Voyager 1 returned 60 frames back to earth, which were stored in an on-board tape recorder after being taken. One of the pictures returned was of Earth showing up as a pale blue dot in the grainy photograph.

The Pale Blue Dot was also shown as a portion of a wide-angle image containing the sun and the region of space where the Earth and Venus were at that time. The wide-angle image was inset with two narrow-angle pictures centered on Earth and Venus. It was taken with the camera's darkest filter (a methane absorption band), and the shortest possible exposure (5 milliseconds) to avoid saturating the camera's vidicon tube with scattered sunlight. The sun appears small in the sky as seen from Voyager's perspective at the edge of the solar system, but is still eight million times brighter than the brightest star in Earth's sky – Sirius. The image of the sun in the photograph is far larger than the actual dimension of the solar disk. The result of the brightness is a bright burned-out image with multiple reflections from the optics in the camera. The rays around the sun are a diffraction pattern of the calibration lamp which is mounted in front of the wide-angle lens. The image was composed of 640,000 individual pixels. In the photograph, Earth lies in the center of one of the scattered light rays resulting from taking the image with a small angle between the Sun and the Earth. Earth takes up less than a single pixel (only 0.12 pixel in size as referred to by NASA). The radio signal which carried the image back to Earth, travelling at the speed of light, took nearly 5 hours and 30 minutes to reach Earth. As the Deep Space Network was preoccupied with the Magellan and Galileo missions, the image reception was delayed. Detailed analysis of the Pale Blue Dot also suggested that Voyager 1 detected the moon as well, but it is too faint to be seen without special processing.