An image of the grand design spiral galaxy M100 obtained with the second generation Wide Field and Planetary Camera.
The WFPC-2 will allow the Hubble Space Telescope to be used to attack one of the most fundamental questions in science: the age and scale of the universe. Astronomers have many "yardsticks" for measuring the scale of the universe, but lack a good knowledge of how long these yardsticks really are. M100 is a member of the Virgo Cluster of galaxies. By allowing astronomers to resolve and measure individual stars in the Virgo Cluster -- in particular a special type of star called Cepheid variables, which have well known absolute brightnesses -- HST observations are expected to provide a crucial measurement of this much needed scale. (Only Space Telescope can make these types of observations. Cepheids are too faint and the resolution too poor, as seen from ground-based telescopes, to separate the images in such a crowded region of a distant galaxy.)

This sequence of pictures shows successive steps in optical improvement from ground based telescopes to the newly improved Hubble Space Telescope and demonstrates the unique capability of the repaired HST. HST offers superb resolution, which allows astronomers to distinguish individual stars in other galaxies. The resolution also allows very faint stars to be seen. This set of pictures demonstrates that the repaired HST can see stars which could never before be detected.

Upper Left: The new WFPC-2 is able to resolve individual bright stars in this Virgo Cluster galaxy, which are indicated by arrows. At this early image, it is not sure if the marked stars are bright Cepheid variables, from which one could derive a distance. Over the following months, however, astronomers were successful in identifying over 20 of these variable stars with the refurbished HST, and determined this galaxy's distance to be 56+/-6 million light years. Upper right: An exposure of the same field in M100, but taken with the old WPFC-1 and the less sharp, uncorrected pre-refurbishment HST optics, on Nov 23, 1993. The arrowed stars are no more visible. The brighter spots are probably clusters. Lower left: Same view, computer enhanced. Still the bright individual stars stay hidden in the diffuse background. Lower right: An image from the Earth-bound 200-inch telescope on Mt. Palomar, taken under conditions slightly better than average. Even the rawer details visible with the WPFC-1 remain obscured in a diffuse nebulous background.

Last Modification: 19 Apr 1998