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.
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.
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.
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.”