After decades of exciting breakthroughs, Princeton astronomers are enjoying a new explosion of discoveries

Messier 51, as observed in the Sloan Digital Sky Survey, is actually two galaxies in collision. The impact, which will take 100 million years to complete, creates the spiral arms and the spray of stars visible at the right. Known as the Whirlpool Galaxy,
Messier 51, as observed in the Sloan Digital Sky Survey, is actually two galaxies in collision. The impact, which will take 100 million years to complete, creates the spiral arms and the spray of stars visible at the right. Known as the Whirlpool Galaxy, Messier 51 is 23 million light-years away from Earth.
Courtesy Robert Lupton *85 and the Sloan Digital Sky Survey (SDSS) Collaboration
J. Richard Gott *73 on his “astronomical carpet.” The map on the carpet appears in the forthcoming book, “Sizing Up the Universe: The Cosmos in Perspective,” co-authored by Gott and Professor Robert Vanderbei.
J. Richard Gott *73 on his “astronomical carpet.” The map on the carpet appears in the forthcoming book, “Sizing Up the Universe: The Cosmos in Perspective,” co-authored by Gott and Professor Robert Vanderbei.
Ricardo Barros

One breezy December afternoon in 1882, faculty astro­no­mer Charles Young fired up the gas engine that powered Halsted Observatory’s metal dome and turned the dials of the new, 30-foot-long telescope, fourth-largest in the world. Then he waited nervously for a celestial event that would not happen again for 122 years, the transit of Venus — the passage of that planet between the Sun and Earth. To his delight, the Sun emerged from a veil of clouds just in time. “The halo of the planet’s atmosphere was simply exquisite,” Young marveled, “arching over the dark globe as if the Sun were reaching out ­delicate arms of light to embrace her daughter.”

Although astronomy had been taught on campus since the 1780s, that thrill­ing moment marked the true beginning of serious astronomical research at Princeton. The talented Young, recently brought down from Dartmouth, would go on to train one of the greatest scientists of the 20th century, Henry Norris Russell 1897 *1900, who succeeded him as professor and established Princeton as a leading center for theoretical astronomy. The pace of discovery has not slowed since. When Peyton Hall, the home of Princeton astrophysics, was renovated two years ago, it got a 50-foot decorative carpet that copies a “logarithmic-scale” map created by Professor J. Richard Gott *73: “Every step is a factor of 10 farther away,” he says, taking you from Earth to Big Bang in 17 easy strides. Walk­ing down it, Gott enthusiastically lists the many achievements made by Prince­tonians, from the co-discovery of the “Great Wall” of galaxies by Margaret Geller *75 to the breakthrough identification of the cosmic microwave background.  

That record of achievement continues: This year’s Shaw Prize — the “Asian Nobel” — went to three scientists who worked on the Wilkinson Microwave Anisotropy Probe satellite, or WMAP, named after a late Princeton scientist. Two of the three winners, Lyman Page and David Spergel ’82, currently are on the faculty.

The talented Charles Young, brought down from Dartmouth, would go on to train one of the greatest scientists of the 20th century, Henry Norris Russell 1897 *1900 (pictured), who succeeded him as professor and established Princeton as a leading ­center fo
The talented Charles Young, brought down from Dartmouth, would go on to train one of the greatest scientists of the 20th century, Henry Norris Russell 1897 *1900 (pictured), who succeeded him as professor and established Princeton as a leading ­center for theoretical astronomy.
George Karger/Time & Life Pictures/Getty Images

All this success has come in spite of a severe obstacle: The Garden State is lousy for stargazing. The clouds that nearly spoiled Young’s observations of Venus later ruined the transit of Mercury for him in 1894: “The weather permitted us to do nothing,” he lamented. Halsted Observatory would prove unusable 265 nights a year. FitzRandolph Observatory, which replaced it in 1934, saw less and less use as the decades went by, especially once suburban sprawl filled the sky with light pollution. After a last hurrah in looking for blinking lasers from extraterrestrial civilizations, FitzRandolph was shut down forever two years ago.  

“Our location means we have had to use our wits,” says theoretical astrophysicist Jeremiah Ostriker. The department has responded by forging creative partnerships with distant facilities. Today, Princeton owns a 16 percent timeshare in the observatory at Apache Point, N.M., one of the darkest sites in the continental United States. In addition, it recently has begun a relationship with Subaru Telescope in Hawaii, atop a 13,760-foot volcano in the middle of the Pacific — places far different from old Halsted Observatory, bathed by the gas-lit streetlamps of University Place.

Lyman Spitzer *38’s ideas led eventually to the Hubble Space Telescope, after decades of wrestling with bureaucrats and ­fighting to keep his vision alive. Now in its 20th year, Hubble has been used by 4,000 astronomers worldwide to make nearly a ­mil
Lyman Spitzer *38’s ideas led eventually to the Hubble Space Telescope, after decades of wrestling with bureaucrats and ­fighting to keep his vision alive. Now in its 20th year, Hubble has been used by 4,000 astronomers worldwide to make nearly a ­million observations, and NASA proudly calls it “the most significant advance in astronomy since Galileo’s telescope.”
Al Fenn//Time Life Pictures/Getty Images

Astronomers come in two types, observers and theorists. Because observing is nearly hopeless in New Jersey, Princeton’s Department of Astrophysical Sciences has concentrated on the latter and has been for generations perhaps the best theoretical program anywhere — partly through powerful synergies with Princeton’s physics department and the Institute for Advanced Study, going back to Einstein.  

Yet the department always has maintained a fruitful presence in observational astronomy. Some of the senior members of today’s faculty, including Ostriker, were handpicked by Russell’s student Lyman Spitzer *38. When Spitzer was hired in 1947, he insisted that a brilliant astronomer, Martin Schwarzschild, come along and that the two of them be allowed to develop “extra-terrestrial observatories” that would float high above the clouds — a concept that would have astounded their 19th-century predecessors. Spitzer’s ideas led eventually to the Hubble Space Telescope, after decades of wrestling with bureaucrats and fighting to keep his vision alive. Now in its 20th year, Hubble has been used by 4,000 astronomers worldwide to make nearly a million observations, and NASA proudly calls it “the most significant advance in astronomy since Galileo’s telescope.”

In the late 1950s, long before Hubble was feasible, Schwarzschild led the futuristic Project Stratoscope, which dangled huge telescopes from balloons, then wafted them up to a height of 20 miles, above most of the earth’s atmosphere. Cutting-edge technology made this possible — namely, remote pointing and focusing of the instrument.   (“I don’t want a man in my balloon,” said Schwarzschild, a German émigré. “He can’t do anything but wiggle it.”) “Princeton first demonstrated you could build an electronic recording medium that could radio a signal to the ground,” says senior research astronomer Edward Jenkins, who later worked closely with Schwarzschild. Without that innovation, Hubble never could have happened.  

Project Stratoscope faced immense practical difficulties. The unwieldy balloon and payload were together taller than the Washington Monument. Launched at night in Texas, they drifted and wobbled with the winds, then fell to earth at dawn several states away. One trial balloon ran amok and had to be shot down by Navy jets over the Atlantic. Schwarzschild’s herculean efforts provided the clearest pictures yet taken of sunspots (many of us saw them in childhood textbooks) and proved the extreme dryness of Mars — no “canals,” as some had speculated. Yet they also showed how unfeasible balloons were, and plans quickly shifted to satellites.  

Spitzer led the Princeton team that designed the first really successful “orbiting astronomical observatory,” Copernicus, launched by NASA 500 miles up in 1972. Measuring the ultraviolet spectrum, almost impossible to do beneath Earth’s soupy atmosphere, it discovered new pulsars and proved the existence of black holes. “Copernicus paved the way to the extreme success we’ve had with Hubble,” says NASA’s Ed Weiler, who worked at Princeton in 1975–78 before becoming Hubble’s chief scientist.  

Princeton investigators then redirected their attention from ultraviolet to microwave radiation, a decision that would yield stunning results and eventually turn cosmology on its head. In the physics department, professor David Wilkinson had participated in one of the great discoveries of the century: the surprise detection of the cosmic microwave background, remnant heat from the Big Bang. First noticed in 1963 at Bell Labs in New Jersey as an annoying hum interfering with a new radio receiver, it was correctly identified by Wilkinson and colleagues at Princeton — although the subsequent Nobel Prize went only to the Bell Labs scientists. Wilkinson helped to create a satellite to map this radiation, Cosmic Background Explorer (COBE), launched in 1989. After his death in 2002, his name was applied to COBE’s successor satellite, WMAP (Wilkinson Microwave Anisotropy Probe), which is 45 times more sensitive — “anisotropy” meaning the tiny temperature fluctuations it measures.

University astronomer Jim Gunn, often called the greatest astronomical instrument designer in the world, created a big, 3.5-meter telescope with a twist: It was the first ever designed for operation via the Internet.
University astronomer Jim Gunn, often called the greatest astronomical instrument designer in the world, created a big, 3.5-meter telescope with a twist: It was the first ever designed for operation via the Internet.
Frank Wojciechowski

Princeton cosmologist Lyman Page has been involved with WMAP from the very beginning, when he happened to walk past Wilkinson’s office at 217 Jadwin Hall in 1990: “He called me in and said, ‘Do you want to work on a satellite?’ ” Page did. Because the microwave background was emitted about 380,000 years after the birth of the universe, WMAP functions as a time machine, looking back nearly to the beginning of everything. Astronomers long have dreamed of dating the universe precisely; in 1953, Spitzer and Schwarzschild used data from the 200-inch Mt. Palomar telescope in California to show that it must be twice as old as the previously accepted date of 2 billion years. But now we know it is much older than that: Among WMAP’s measurements is a date of 13.75 billion years.  

As it ages, the universe is cooling and growing darker, WMAP shows, with a huge increase in “dark energy,” a hypothetical force cosmologists invoke to explain the recent speeding up in its expansion. WMAP has borne out the theories of cosmologists Ostriker and Paul Steinhardt, who presciently proposed dark energy in a 1995 paper (see “The Cosmic Apocalypse,” Feb. 11, 2009). “It’s one of the fundamental mysteries of physics,” Page says, and he and his faculty colleagues are debating it vociferously.  

Today, at the end of its nine-year mission, which took it a million miles from Earth, WMAP has garnered vast praise from the scientific community worldwide. “It gave us the standard model of cosmology,” Page says, sitting at his desk in the office that was once Wilkinson’s. “I think the field really changed then, with these unassailable measurements. To be a viable cosmological model, you now have to agree with the WMAP data.”

As electrifying as “space astronomy” has proven lately, ground-based observation remains important. Starting in the late 1980s, Princeton collaborated with other universities in putting together the state-of-the-art observatory at New Mexico’s Apache Point. Princeton astronomy professor Jim Gunn, often called the greatest astronomical instrument designer in the world, created a big, 3.5-meter telescope with a twist: It was the first ever designed for operation via the Internet. Gone are the cheerless nights when Charles Young toiled alone, shivering, in the dark confines of Halsted Observatory, nearly deafened by the thunderous rumbling of the metal dome as it rolled over 40 pulleys set in a ring on a circular track of railroad rails. Today, Apache Point streams data instantly to scientists across the country, who sip coffee at their desks as they control the telescope using mouse and keyboard.  

It’s comparatively simple to log in and check the same astronomical object for just 20 minutes, night after night, a task Young would have found exhausting with his cumbersome equipment. “I’ve even ‘observed’ in my kitchen, using my laptop,” says astrophysics professor Michael Strauss. He and Xiaohui Fan *00 used the telescope to discover what was at the time the most distant quasar known in the universe, some 12 billion light-years away — and they did it sitting in the basement of Peyton Hall at 1:30 a.m. one Thanksgiving.  

Apache Point also is home to the revolutionary Sloan Digital Sky Survey, which uses another Gunn-designed telescope. This one resembles an enormous steel cube loaded with the most complex camera hitherto built — a 700-pound behemoth that took six years to assemble in the Peyton Hall basement. In what Princeton astrophysicist Edwin Turner calls “a strip mining of the sky,” it swept the heavens, recording everything it saw, and by 2008 it had produced the most elaborate map in human history. A year later, Gunn was awarded the National Medal of Science, becoming the 19th Princetonian to win that prestigious prize — a rarified club that includes Schwarzschild, Spitzer, and Ostriker.  

Unlike traditional star maps on photographic film, this one is in three dimensions, an astonishing advance. The Sloan Digital Sky Survey telescope uses spectra of light to measure distances to all kinds of celestial objects, recording them in vast digital files. Astronomers have studied spectra for generations — Young painstakingly used Princeton’s spectroscope, then the best in the world, to prove that sunspots were not lumps of soot — but the Sloan survey analyzed such spectra at incredible speed, 5,000 every night. It established the precise distance to a million galaxies and showed that they assemble themselves into immense, meandering “walls,” forming a kind of fibrous structure for the universe. In addition, it identified 100,000 quasars, 10 times as many as previously were known, along with a half-million new asteroids.

 “Because planets are ­dazzled out by their star, you need to use some clever tricks to find them,” says Princeton astrophysicist Gillian Knapp.
“Because planets are ­dazzled out by their star, you need to use some clever tricks to find them,” says Princeton astrophysicist Gillian Knapp.
Frank Wojciechowski

“The data are of superbly high quality,” says Princeton astrophysicist Gillian Knapp, who was closely involved with the project. “It is a magnificent example of what happens if you do something right.” Scientists already have written an unprecedented 3,200 papers based on it. Ushering in a new era in astronomy, the data are available in fully processed, ready-to-use form on the Internet. Astronomers without access to a powerful telescope, or amateurs tired of suffering frigid nights and ever-increasing light pollution, can click on a site called SkyServer and instantly explore Sloan’s vast resources. With a few keystrokes on a home computer, a full-color, minutely detailed, virtual universe springs spectacularly to life. “There have been several important discoveries made by amateurs using Sloan,” Knapp says, including one by a young Dutch schoolteacher who stumbled upon an ionized-gas cloud new to science.

Partly to share burgeoning costs, astronomy today is about partnerships. Princeton astronomers have long benefited from proximity to Washington, D.C., going all the way back to Young’s day, when Uncle Sam provided the photographic plates Young used to record the transit of Venus. Princeton often has worked with NASA’s Goddard Space Flight Center in Maryland, including on WMAP.   Increas­ingly the partnerships are international, however — meshing with the University’s new efforts to be more global. An exciting new initiative began in 2009 with a 10-year agreement with the National Astronomical Observatory of Japan: Princeton scientists will use the huge new Subaru Telescope in Hawaii, the most expensive ground-based instrument in the world, to explore the farthest corners of the universe.  

They plan to study dark energy and the equally perplexing dark matter. “One of the most confusing questions that has bedeviled us a long time is, How is dark matter distributed?” says Strauss. “Einstein predicted that gravity can bend light. We will use Subaru to measure the shapes of tens of millions of galaxies, looking for distortions — making the effects of the dark matter visible.”

Another big task for Subaru is the search for “exoplanets” orbiting distant stars.   “Every star may have planets around it,” Russell speculated in 1926, but only recently have they actually been detected — some 460 since 1992. In his first few months working with Subaru, Princeton postdoc Mike McElwain already has discovered an exoplanet, one of just 10 that have ever been “directly observed” and their snapshot taken (because planets are so small, they usually are identified only by their star’s faint gravitational wobbling). The nature of this new, cherry-red object is uncertain — with a much greater mass than Jupiter, it may be a brown dwarf rather than a planet — but what makes it exciting is that it orbits a quite small star, only the size of our Sun.

This refurbished 1877 Alvan Clark telescope is believed to have been used by Professor Charles Young in his teaching. It now hangs in the ­conference room in Peyton Hall.
This refurbished 1877 Alvan Clark telescope is believed to have been used by Professor Charles Young in his teaching. It now hangs in the ­conference room in Peyton Hall.
Ricardo Barros
Peyton Hall groundbreaking in 1966; from left, University Financial Vice President and Treasurer Ricardo Mestres, Bernard Peyton 1917, Dean of the Faculty J. Douglas Brown, and Lyman Spitzer *38.
Peyton Hall groundbreaking in 1966; from left, University Financial Vice President and Treasurer Ricardo Mestres, Bernard Peyton 1917, Dean of the Faculty J. Douglas Brown, and Lyman Spitzer *38.
Princeton University Archives
Peyton Hall on Ivy Lane, the modern home for the astrophysics department, hosts a monthly open house for the public to view the night sky through a 12-inch Schmidt-Cassegrain telescope.
Peyton Hall on Ivy Lane, the modern home for the astrophysics department, hosts a monthly open house for the public to view the night sky through a 12-inch Schmidt-Cassegrain telescope.
Ricardo Barros


McElwain and colleagues dream of finding Sun-like stars circled by Earth-like planets. It’s part of that ancient astronomical quest, the search for extraterrestrial life.   “There are probably millions of planets with a variety of life on them,” Russell said back in 1924, and he used the 100-inch Mount Wilson telescope in California to seek chemical traces of organic activity in the atmosphere of Venus. Oxygen above Mars seemed proof to him, for a time, of “vegetable life” there.  

Russell’s speculations won him a place in pop culture: In 1938, he was transformed into “world-famous astronomer Richard Pierson” in Orson Welles’ sensational War of the Worlds radio broadcast. “I’m standing in a large semicircular room, pitch-black except for an oblong split in the ceiling,” intoned the reporter, supposedly on location at FitzRandolph Observatory. “Professor Pierson stands directly above me on a small platform, peering through the giant lens.” The astronomer soon would learn, most unpleasantly, that Martians weren’t vegetables after all.  

Rather than wait for extraterrestrials to crash-land at Grover’s Mill, today’s Princeton scientists are actively looking for the exoplanets they (might) call home. “Because planets are dazzled out by their star, you need to use some clever tricks to find them,” says Knapp, who is working on the Subaru project. The tough task of locating planets small and rocky enough to harbor life may get a boost from a proposed NASA satellite, Terrestrial Planet Finder. Here, too, Tigers are playing a central role. In his E-Quad lab, engineer Jeremy Kasdin and fellow researchers are trying to boost the resolution of space telescopes. Knowing that even tiny improvements might make all the difference, they are tweaking coronagraphs (used to block the light of the nearby star so that the planet can be seen) and using clever “adaptive optics” that correct for a telescope’s inevitable flaws in vision.  

In this century, NASA’s Weiler predicts, we will find proof of extraterrestrial life, perhaps from a space telescope trained on an exoplanet. “I dream of someday having enough resolution,” he jokes, “to see their lights go on at night.”  

W. Barksdale Maynard ’88 is the author of Woodrow Wilson: Princeton to the Presidency and the forthcoming Princeton: An Architectural History of the Campus.