NASA's Hubble Space Telescope has been capturing stunning images from around the universe for nearly 20 years. For much of that time, the JPL-designed and -built Wide Field and Planetary Camera 2 has been taking many of the most famous Hubble pictures, recording razor-sharp images of faraway objects in relatively broad views.
As part of the Hubble Servicing Mission in May 2009, this camera will be removed by Space Shuttle astronauts and replaced with a new camera, called Wide Field Camera 3. This new camera is designed to ensure that Hubble maintains its unique imaging capabilities until the end of its mission, while at the same time advancing its survey and discovery capability through a combination of broad wavelength coverage, wide field of view and high sensitivity.
The original Wide Field/Planetary Camera was installed on the Hubble telescope when it was first launched into Earth orbit on a space shuttle on April 24, 1990. Scientists soon discovered, however, that a tiny error in the curvature of the space telescope's main mirror made it impossible to focus images sharply. Fortunately, JPL engineers determined that by changing the optics of the camera instrument, the telescope's problem could be overcome. The next camera instrument, called the Wide Field and Planetary Camera 2, was installed on Hubble by spacewalking astronauts on a space shuttle mission launched on December 2, 1993. This brought Hubble's vision to perfect focus, and over the next few years the space telescope has relayed phenomenal pictures and made possible a variety of discoveries.
From Pixels to Pictures
The Wide Field and Planetary Camera 2 doesn't use film to record its images. Instead, four postage stamp-sized pieces of high-tech circuitry called Charge-Coupled Devices (CCDs) collect information from stars and galaxies to make photographs. These detectors are very sensitive to the extremely faint light of distant galaxies. They can see objects that are 1,000 million times fainter than the naked eye can see. Less sensitive CCDs are now in some videocassette recorders and all of the new digital cameras. CCDs are electronic circuits composed of light-sensitive picture elements (pixels), tiny cells that, placed together, resemble a screen-door mesh. Each of the four CCDs contains 640,000 pixels. The light collected by each pixel is translated into a number. These numbers (all 2,560,000 of them) are sent to ground-based computers, which convert them into an image.
Why Do the Pictures Look So Funny?
The unique design results in the stair-step appearance of many of its images (see the Eagle Nebula at the top of the right column on this page). The "heart'' of the instrument consists of four cameras: one high-resolution "planetary" camera and three "wide-field" cameras. Although the planetary camera can see only a small region of the sky, it packs a punch — compacting the same number of pixels into a smaller area results in finer-detailed images. The difference between the wide-field detectors and the planetary camera is like the difference between a wide-angle lens and a telephoto lens.