AMHERST, Mass., April 17 -- The vast archive of images and data resulting from the Two Micron All-Sky Survey (2MASS), the most thorough, high-resolution survey of the sky, has been completed. The archive, which features some five million images, is now available online for scientists and sky watchers. The project, which relied on twin infrared telescopes, was led by astronomers at the University of Massachusetts (UMass) Amherst. The survey was conducted using infrared light to peer through the dust within and beyond our Milky Way galaxy, enabling astronomers to detect and identify more than 500 million objects, primarily stars, but including galaxies, asteroids and comets. The project used two dedicated 1.3-meter telescopes, one at Mount Hopkins, Ariz., the other at the Cerro Tololo Inter-American Observatory in Chile. Observations began in 1997 and concluded in early 2001. Scientists have spent the past year completing an analysis of the entire sky. The survey produced two major catalogs detailing nearly half a billion objects. "The aim of the 2MASS science team was to produce a comprehensive map of the sky that could be shared with the rest of the science community," said Martin Weinberg, a UMass astronomer who has been closely involved in the project. "We as scientists were motivated to do the project by the promise of the science that will result from it in coming years. This is a major astronomical archive that will have context and worth for decades." "The sky has been surveyed by astronomers before, but by looking at infrared light 2MASS was able to detect some objects that were invisible at optical wavelengths," said Stephen Schneider, another UMass astronomer who is closely involved in the project. "Even known astronomical sources reveal many new things about themselves in infrared light. There are hundreds of discoveries waiting to be made in this immense database." "This survey was an old human activity, but with a modern twist," said project manager Rae Stiening at UMass. "Just as English admiralty sent Captain Cook and others to map the world, this new survey has mapped the nearby universe." "This survey will change the way astronomy is conducted and the types of experiments that can be carried out, because astronomers can now sit at their desk and have data for any spot on the sky literally at their fingertips, without going to a telescope," said Roc Cutri, the survey's project scientist at the Infrared Processing and Analysis Center of the California Institute of Technology and NASA's Jet Propulsion Laboratory, Pasadena, Calif. "It also makes astronomy more open to the public, providing beautiful pictures and serving as a powerful educational tool." The survey's findings include: Confirmation of a new class of stars, known as brown dwarfs, which are very red, and too cool to be seen by previous methods; A more complete understanding of our Milky Way's structure; A new view of the "nearby" universe, and the way that galaxies cluster together over distances of hundreds of millions of light years The most detailed database ever of location, brightness, color and position of asteroids in the nearby universe. The findings are now available to scientists and sky watchers through two catalogs that are essentially final inventories of stars and galaxies throughout our sky. The first identifies "point sources" throughout the sky; that is, all discernable sources of light, from the very brightest stars to sources that are tens of thousands of times fainter. The second catalog of extended sources includes over a million galaxies and nebulae, some at a distance of billions of light years. The galaxy catalog can be downloaded into an existing PC. The point-source catalog, which is on six DVD Roms, requires a specialized server, but building the server is well within the financial means of research universities, Weinberg said. "The public will 'ooooh and aaaah' at the pictures, while scientists will mine the data for decades, learning more about our Milky Way galaxy and hundreds of millions of its stars, and about the millions of galaxies in the nearby universe," said Michael Skrutskie, principal investigator for 2MASS. Skrutskie, with the University of Virginia, Charlottesville, was formerly with UMass. 2MASS is a collaboration between UMass Amherst and the Infrared Processing and Analysis Center. The university was responsible for design, construction and operation of the survey cameras and telescopes, as well as the observations and acquisition of images. The center developed the software system that converted the nearly 25 terabytes of raw digital data into images and catalogues. The survey is primarily funded by NASA's Office of Space Science, with additional funding from the National Science Foundation. For more information, and to view 2MASS Telescope images, visit: irsa.ipac.caltech.edu/index.html; pegasus.astro.umass.edu