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Hubble: first light with a second eye.

Hubble: First light with a second eye

Two stars in a cluster known as NGC 188 provided "first light" for an image (far right) taken June 17 by the Hubble Space Telescope's most sensitive eye. Astronomers expect the instrument, called the faint-object camera (FOC), to detect stars and other celestial objects as dim as 28th magnitude -- so faint that telescope on Earth cannot detect them at all.

NGC 188 is 630 times brighter than that, says F. Duccio Macchetto of the European Space Agency in Paris and the Space Telescope Science Institute at Johns Hopkins University in Baltimore. To prevent an overexposure, engineers, had to use filters to cut the instrument's sensitivity by about seven magnitudes.

The FOC has such a small field of view that "the whole team ... broke out the champagne when we saw the very stars we had expected to see in the FOC image," Macchetto says.

The image on the left shows that far more distorted appearance of the same two stars as viewed from the ground through the turbulence of Earth's atmosphere. Astronomers took this photo using the 2.5-meter Nordic Optical Telescope on the Canary Island of La Palma.

The two stars -- imaged as engineers worked to sharpen the Hubble's focus and to reduce the vibrations affecting it -- were chosen because astronomers had accurate information on the positions and brightnesses of stars in their cluster. NGC 188, a part of the Milky Way galaxy, is about 5,000 light-years from Earth and located about 4[degrees] from the position of the North Star. Astronomers estimate its age at about 12 billion years, nearly that of the Milky Way galaxy.

The space telescope's other imaging instrument, called the wide-field and planetary camera, saw its "first light" on May 20 (SN:5/26/90, p.325).
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Title Annotation:Hubble Space Telescope
Author:Eberhart, Jonathan
Publication:Science News
Date:Jun 30, 1990
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