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The model of the universe allows an observer to travel the galaxies.

It's fair to say that Dan Long has seen more of the universe than anyone but God.

Month after month, year after year, Long has sat in a windowless room atop a windy mountain peak, watching the heavens scroll by on 12 monitors connected to the Apache Point Observatory's 98-inch telescope.

He has seen stars, galaxies and clusters of galaxies banded together like giant herds of animals on an unending savanna roll by. Less frequently, exotic denizens of deep space have popped up - blinding quasars and supernovae, flaring up as brightly on the bank of TV screens as entire galaxies.

"You get a sense of how big it is out there," said Long, 46, a genial astronomer. "If you didn't already feel small, this would do it."

This summer, after eight years charting the cosmos, Long and his colleagues completed the deepest, most comprehensive map of the heavens ever produced.

Known as the Sloan Digital Sky Survey, it is a three-dimensional model of the universe that allows an observer to travel, as if by rocket ship, from the dwarf galaxies hugging the skirts of the Milky Way to the most distant quasars, billions of light-years away.

In its 5 terabytes of data are 217-million individual objects, including 800,000 galaxies (which themselves contain billions of stars and planets) and 100,000 quasars - objects once so rare and strange that they weren't detected until 1962.

"Nobody's ever done anything like this before," said Bruce Gillespie, administrator of the Astrophysical Research Consortium, made up of 300 astronomers who helped carry out the $100-million sky-mapping project. "They'll still be looking at this data in 50 years."

Among the survey's notable achievements has been helping to confirm the existence of dark energy, the mysterious force believed to be causing the universe's expansion. The survey also has shown that the universe is flat, and it has given more weight to the big-bang theory, which says the universe began with a single explosion that was followed by rapid inflation that continues to this day.

But perhaps its greatest achievement has been bringing a sense of order to the seemingly undefined vastness of the universe.

Like the great cartographers of the past who turned apparently limitless seas and unknown continents into familiar terrain, the Sloan astronomers have struggled to make that most unfathomable of places - the universe - navigable.

"The joke we've always had is that if you rotate the galaxies in just the right way," Gillespie said, "you'll see the face of Elvis."

The Sloan survey was the brainchild of Jim Gunn, 69, an astrophysicist at Princeton University and one of the world's leading experts on galaxy formation.

Before Sloan, the most authoritative map of the heavens in visible light was the Palomar Observatory Sky Survey, which from 1950 to 1957 mapped the Northern Hemisphere's night sky with its 48-inch Samuel Oschin Schmidt telescope. The result was a master reference work for amateur and professional stargazers alike.

But by the mid 1980s, it was out of date. Radio, X-ray and infrared astronomers had launched their own sky surveys, some of which surpassed Palomar in breadth and detail.

"There was a little embarrassment" among optical light astronomers, Gunn said. "We were decades behind."

Another motivating factor, Gillespie said, was a seminal discovery in the 1980s: Galaxies, once thought to be the largest structures in the universe, sometimes formed clusters. "This was a hint of larger structures in the universe," Gillespie said.