PUBLIC INFORMATION OFFICE JET PROPULSION LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY NATIONAL AERONAUTICS AND SPACE ADMINISTRATION PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011 PHOTO CAPTION January 13, 1994 This sequence of pictures shows successive steps in optical improvement from ground-based telescopes to the newly improved Hubble Space Telescope. The images demonstrate that the repaired telescope can see stars that could never before be detected. At upper left is an outer region in the galaxy M100 as imaged by the telescope's second-generation Wide Field and Planetary Camera. The WFPC-II incorporates modified optics that correct for the aberration of the telescope's primary mirror. This image demonstrates one of the most important servicing achievements -- the ability to detect and measure the light from individual faint stars in distant galaxies. The stars indicated by the arrows have the approximate brightness of special yardstick stars called Cepheid variables in M100. While these specific stars may not be Cepheids, astronomers expect that repeated measurements of hundreds of similarly bright stars spread throughout the galaxy will turn up several dozen Cepheids. By accurately measuring the brightness of these "standard candles," astronomers will use the WFPC-II to determine an accurate distance to M100. When combined with similar measurements for other galaxies, this distance will provide a crucial link in the chain that astronomers use to determine the expansion rate, age and size of the universe. At upper right in an image taken by the WFPC-I on November 27,, 1993, just a few days before the Hubble servicing mission. WFPC- I's resolution represents a significant improvement over what can be seen from the ground. However, images made before the servicing mission revealed only the brightest objects seen in the frame to the left. At lower left is a panel showing the computer-processed WFPC-I image, using a technique commonly employed to improve Hubble images taken before the servicing mission. Although processing can significantly sharpen up features, they cannot recover faint objects; many stars revealed in the WFPC-II image cannot be seen or measured in the reconstructed WFPC-I image. At lower right is an image of the same region in M100 taken with the 5-meter (200-inch) Hale telescope at Mt. Palomar in California. The resolution is just under an arc-second, slightly better than typical nigh̉t-sky conditions for ground-based observing. The Jet Propulsion Laboratory developed the Wide Field and Planetary Camera-II for NASA's Office of Space Science. #####