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News Release 22 of 38

June 4, 2001 12:30 PM (EDT)

News Release Number: STScI-2001-18

Bigger, Better Catalog Unveils Half a Billion Celestial Objects

An American Astronomical Society Meeting Release

June 4, 2001: It's a very big universe out there, and an astronomer's work is never done when it comes to simply counting and cataloging the sheer number of stars in the heavens. Completing a seven-year effort at digitizing the entire sky for a second time, astronomers at the Space Telescope Science Institute and the Osservatorio Astronomico di Torino are releasing the Guide Star Catalog II. This new version, which replaces the historic 1989 catalog, provides important information on nearly one-half billion stars over 20 times as many as the original Guide Star Catalog.

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Q & A: Understanding the Discovery

  1. 1. How is this catalog useful to astronomers?

  2. The new catalog provides a census of every star in the heavens with luminosities as bright as the 19th magnitude, while the previous catalog only went to the 15th magnitude. (The human eye can see celestial bodies as dim as the sixth magnitude. The very faintest objects ever seen are at 30th magnitude.) For the first time, the catalog is in living color, which provides an invaluable new dimension of stellar information.

    The catalog will serve as a bigger and better "roadmap" for the Hubble telescope to use when aiming its Space Telescope Imaging Spectrograph, which can only look at very faint objects (below the 18th magnitude). Pairs of guide stars are used as reference points in the sky for the telescope to lock onto for stability during observations.

    But the catalog also will be an invaluable reference for amateur and professional astronomers to plot sky charts, search for stars that vary in brightness, execute stellar population studies, and perform multi-object spectroscopy.

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Credit: NASA, the DSS-II and GSC-II Consortia (with images from the 'Palomar Observatory-STScI Digital Sky Survey of the northern sky, based on scans of the Second Palomar Sky Survey are copyright 1993-1999 by the California Institute of Technology)