On the right is part of the first image taken with NASA's Hubble Space Telescope's (HST) Wide Field/Planetary Camera. It is shown with a ground-based picture from Las Campanas, Chile, Observatory of the same region of the sky. The Las Campanas picture was taken with a 100-inch telescope and its typical of high quality pictures obtained from the ground. All objects seen are stars within the Milky Way galaxy.
The images of the stars in the ground-based picture are fuzzy and in some cases are overlapping, because of smearing by the Earth's atmosphere. The same stars in the HST frame are sharper and well resolved, as shown by the double star at the top of the image. By avoiding the Earth's atmosphere, the HST gives sharper images and better resolution. In this early engineering picture, the HST images are roughly 50 percent sharper than the ground-based images.
Technical Details: The first image taken with the HST is intended to assist in focusing the telescope. The region observed is centered on the 8.2 magnitude star HD96755 in the open cluster NGC 3532, in the southern constellation Carina. Identical small subsections of the HST and ground-based image pictures were chosen to highlight the difference in resolution. The field shown is approximately 11 x 14 arcseconds in size and does not contain HD96755.
The ground-based image was taken by Dr. Eric Persson at the Las Campanas Observatory in Chile, using the 100-inch DuPont reflector. We thank the Observatories of the Carnegie Institution of Washington for permission to use this picture. The three-second integration was made with a single Texas Instruments charge-coupled device (CCD) of the type used on HST. A broadband visual filter equivalent to the HST filter was used. The small field shown was extracted from an observed area covering 130 arcseconds on a side.
The HST image is a thirty-second exposure taken by the Wide Field/Planetary Camera. The picture shown was extracted from the area observed by the WF-3 OCD using the F555W broadband filter. The measured width of star profiles (FWFM) gives a good indication of the angular resolution. For the Las Campanas picture, the FWFM is 1.1 arcseconds, typical of exposures from the best ground observations. The FWFM of the stars in the HST picture is about 0.8 arcseconds, which points out the remarkable increase in resolution of the HST even at this early stage of the focusing task.