Galaxy M100 resolution comparison

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 afar. 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.

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An outer region in the galaxy M100 as imaged by Hubble Space Telescope's second generation Wide Field/Planetary Camera (WFPC-2). The WFPC-2 incorporates modified optics that correct for the aberration of the primary mirror on the HST. While this image is not as visually spectacular as the image of the core of the galaxy, if demonstrates one of the moat important improvements in the capability of the telescope achieved during the HST servicing mission- the ability to detect and measure the light from individual faint stare in distant galaxies. Note in particular the star indicated by the arrows, which have the approximate brightness expected for Cepheid variables in M100. While these specific stars may not be Cepheids, repeated measurements of hundreds of stars of similar brightness spread throughout the galaxy' are expected to turn up several dozens of Cepheids. By accurately measuring the brightness of these "standard candles," astronomers will use the WFPC-2 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.