Ray Gallery

Pale Blue Dot Revisited

For the 30th anniversary of one of the most iconic images taken by NASA's Voyager mission, a new version of the image known as "the Pale Blue Dot." Planet Earth is visible as a bright speck within the sunbeam just right of center and appears softly blue, as in the original version published in 1990 (see PIA00452). This updated version uses modern image-processing software and techniques to revisit the well-known Voyager view while attempting to respect the original data and intent of those who planned the images. In 1990, the Voyager project planned to shut off the Voyager 1 spacecraft's imaging cameras to conserve power and because the probe, along with its sibling Voyager 2, would not fly close enough to any other objects to take pictures. Before the shutdown, the mission commanded the probe to take a series of 60 images designed to produce what they termed the "Family Portrait of the Solar System." Executed on Valentine's Day 1990, this sequence returned images for making color views of six of the solar system's planets and also imaged the Sun in monochrome. The popular name of this view is traced to the title of the 1994 book by Voyager imaging scientist Carl Sagan, who originated the idea of using Voyager's cameras to image the distant Earth and played a critical role in enabling the family portrait images to be taken. The image of Earth was originally published by NASA in 1990. It is republished here to commemorate the 30th anniversary of the Family Portrait of the Solar System (see PIA00451) and the Pale Blue Dot image in particular. The planet occupies less than a single pixel in the image and thus is not fully resolved. (The actual width of the planet on the sky was less than one pixel in Voyager's camera.) By contrast, Jupiter and Saturn were large enough to fill a full pixel in their family portrait images. The direction of the Sun is toward the bottom of the view (where the image is brightest). Rays of sunlight scattered within the camera optics stretch across the scene. One of those light rays happens to have intersected dramatically with Earth. From Voyager 1's vantage point ? a distance of approximately 3.8 billion miles (6 billion kilometers) ? Earth was separated from the Sun by only a few degrees. The close proximity of the inner planets to the Sun was a key factor preventing these images from being taken earlier in the mission, as our star was still close and bright enough to damage the cameras with its blinding glare. The view is a color composite created by combining images taken using green, blue and violet spectral filters by the Voyager 1 Narrow-Angle Camera. They were taken at 4:48 GMT on Feb. 14, 1990, just 34 minutes before Voyager 1 powered off its cameras forever. Like the original version, this is technically a "false-color" view, as the color-filter images used were mapped to red, green and blue, respectively. The brightness of each color channel was balanced relative to the others, which is likely why the scene appears brighter but less grainy than the original. In addition, the color was balanced so that the main sunbeam (which overlays Earth) appears white, like the white light of the Sun. At its original resolution, the newly processed color image is 666 by 659 pixels in size; this is Figure A. The main image is an enlarged version. The image was processed by JPL engineer and image processing enthusiast Kevin M. Gill with input from two of the image's original planners, Candy Hansen and William Kosmann

Electromagnetic particle shower

Electromagnetic particle shower. Particle tracks (moving from bottom to top) showing multiple electron-positron pairs created from the energy of a high-energy gamma ray photon produced by a neutrino collision. The positron is the anti-particle of the electron, and this process is called pair-creation. Electrons and positrons are charged particles and form these paired spirals as they curve away from each other in a magnetic field. As they do so, they radiate photons, which can in turn produce new electron-positron pairs. This shower of particle creation continues until the energy of the original photon is used up. The region shown here is about 2 metres tall

© GORONWY TUDOR JONES, UNIVERSITY OF BIRMINGHAM/SCIENCE PHOTO LIBRARY

A discussion on the Piltdown skull by John Cooke

Portrait group of well-known British scientists examining the Piltdown skull. This topical painting was exhibited at the Royal Academy in 1915, while debate continued as to whether the bones represented the missing link between man and ape. From left to right in the front row: Professor A.S Underwood, Professor Arthur Keith, Mr. W. P Pycraft and Sir E. Ray Lankester. In the back row can be seen Mr . F.O Barlow, Professor Elliot Smith, Mr. Charles Dawson and Dr. A. Smith Woodward. The Piltdown man was found to be an elaborate hoax in the early 1950s. Date: 1915

© Illustrated London News Ltd/Mary Evans