Stanford Report Online

Stanford Report, October 4, 2000

Art Walker : 'favorite sun' of solar physics


With nothing but stars to guide them, the ancient Polynesians navigated one-quarter of the Earth and discovered heaven in the form of the Hawaiian Islands. When they wanted to return to that paradise, they navigated the open ocean by a single star that hangs reliably over the big island in spring. We know it as Arcturis; they called it Hokule'a, or "the guide star."

Solar physicist Arthur Bertram Cuthbert Walker II has spent a lifetime bridging the space that separates humans from the Sun and from each other. On Sept. 15, Walker got his own day in the sun at a celebration of his achievements sponsored by the departments of Physics and Applied Physics and the African and Afro-American Studies Program.

Professor Calvin Quate (right) and Emeritus Professor Sylvia Wynter (center) were among those who celebrated the achievements of Art Walker (left).
photo: L.A. Cicero

"By your example, you've been the guide star, the Hokule'a, for those of us on the faculty, and for the many students that you've educated here in physics at Stanford," Applied Physics Chair Bob Byer told Walker.

Master of ceremonies Ewart Thomas, professor of psychology, said: "We celebrate Art's innovative research and inspiring teaching in physics, particularly in solar physics, his exemplary contributions to the black community at Stanford, and the abundant love and support Art has given as son, father, husband, cousin and friend to many."

Students, colleagues, friends and family came from near and far to share tales of Walker, who has been a professor of physics and applied physics at Stanford since 1974. Cousins flew in from New Jersey, Georgia and Texas. Members of the Sigma Pi Phi fraternity for black professionals, of which Walker is a member of long standing, drove in from throughout the Bay Area. NASA administrators made the trip from Washington, and the director of the National Optical Astronomy Observatories came from Arizona. Faculty whose research ranged from Ebonics to electronics gathered at the Faculty Club for the reception and dinner along with Walker's wife, Victoria, and two of his three children.

Walker is world renowned for his pioneering use of X-rays and thin films to study the Sun's outermost atmosphere. The excitement engendered by his stunning images of the Sun are a big reason solar physics enjoys a high profile, said NASA program scientist William Wagner: "It's the reason probably that there'll be a new initiative by NASA in this coming year by the name of 'Living with a Star.'" The initiative aims to study solar activity; six telescopes in parallel, Walker-style, will take high-resolution pictures of the Sun every 10 seconds.

For more than a quarter-century, Walker has directed Stanford's student observatory and taught astronomy courses including the popular Applied Physics 15 ("The Nature of the Universe") and Physics 50 ("Observational Astronomy"). He has guided the graduate careers of 13 past Ph.D.s and five current candidates. Among them, seven belong to groups that are underrepresented in physics. His most famous doctoral student is Sally Ride, America's first woman in space.

He has served as associate dean of graduate studies and as a member of graduate student admissions committees for the departments of Physics and Applied Physics. NASA's Phil Sakamoto calls Walker's dedication to bringing underrepresented students into the space sciences program "legendary." A constant stream of his students has received NASA's highly competitive fellowships for graduate student researchers.

"There are no words to express our gratitude to you for being our teacher, mentor, friend and champion," said Dennis Martinez-Galarce, one of nearly a dozen former students at the tribute. "Your Harvard B School style of management gave us the opportunity to think independently, to be creative and to challenge ourselves to understand the research we were performing and the amount of work that was required to accomplish it."

A recent Ph.D. in electrical engineering, Martinez-Galarce now works at Stanford's Hansen Experimental Physics Lab with Walker and physics Professor Blas Cabrera on a project to image energy flows between layers of the Sun's atmosphere.

"Because of Art's efforts, Stanford led the nation among our peer institutions in educating to advanced degrees underrepresented minority students in the physics degree," said Byer.

Walker's recommendations to Congress were instrumental in creating a national solar observatory. And in 1986, President Reagan appointed Walker to serve on the commission that investigated the space shuttle Challenger explosion -- the "JFK event" of a generation -- and concluded that the disaster was preventable.

Alive with activity, the surface of the Sun is characterized by coronal coils, gaseous geysers and other violent visuals revealed by NASA's Multi-Spectral Solar Telescope Array (MSSTA).
Courtesy: NASA/Art Walker

Midway through the September celebration, NASA officials surprised Walker with a Distinguished Public Service Medal in recognition of "four decades of distinguished scholarship, achievements in experimental space sciences and extensive service to NASA and the nation on innumerable advisory and review boards."

The Sun you never knew

Don't stare at the Sun -- you'll go blind, mothers warn their children. But technology that Walker developed with materials scientist Troy Barbee of Lawrence Livermore National Laboratory lets us take a closer look at the Sun than ever before.

While a senior research associate at Stanford's Center for Materials Research in the 1980s, Barbee created multilayered thin films so perfect that they could be considered crystals. This property enabled them to capture images produced by hot solar gas so energetic that it spewed radiation in the extreme ultraviolet end of the spectrum.

"One of the things I have learned over the years as a materials scientist is that materials don't do anything; people do things with materials," Barbee said. "Art has taken those things which I was able to put on the table and use them to demonstrate new science and develop new technologies."

In 1987, Walker developed telescopes and complex instrumentation, mounted them on satellites and launched them into space to escape the interference of the Earth's atmosphere. There they captured the first detailed pictures of the Sun's outermost atmosphere, or corona, the halo of light seen by the unaided eye during a total solar eclipse. Images from the first flight of Walker's solar telescope appeared on the cover of Science magazine on Sept. 30, 1988.

"It was a spectacular achievement," Byer recalled.

"Right away people saw that this technique worked," said Phil Scherrer, a research professor of physics. NASA and European Space Agency scientists designing the Solar and Heliospheric Observatory (SOHO) rushed to put Walker's instrument onboard.

Walker launched 14 telescopes in NASA's first Multi-Spectral Solar Telescope Array (MSSTA) flight in 1991. The second flight, in 1994, had 19 telescopes.

Why so many? A telescope's flight filter only lets in one wavelength of light at a time. "One wavelength is going to look at one temperature in the Sun," explained Scherrer, displaying Walker photos of solar activity at two temperatures -- 25,000 degrees and 1.5 million degrees Kelvin. "To look at different temperatures at different heights in the Sun, you need a whole collection of them. Things happen at all different temperatures at the same time."

Images that show how the Sun's temperature changes in different regions will give scientists a greater understanding of solar activity.

For reasons that still puzzle scientists, the corona is 1,000 times hotter than the Sun's visible surface. A close look reveals that this seemingly benign, fuzzy ball is downright violent.

Hot, electrified gas in the corona produces high-energy particles and solar wind that disrupt the Earth's magnetic field to produce colorful auroras and wreak havoc with telecommunications, electric power, radar and weather.

"The solar wind -- the impingement of charged particles on the Earth -- greatly enhances that amount of lightning we see, and in fact all the great fires in the forests this summer are really tied to [peak solar activity]," Barbee said. "We should understand that, and we should understand how that affects us. What Art has done is going to give us that opportunity."

Walker's technique also has been used in NASA's Chandra X-ray observatory, to study the nighttime sky, and in a worldwide chain of ground stations called the Global Oscillation Network Group (GONG), to study solar activity.

A star is born

Walker's paternal grandfather, James Henry Walker, was a schoolmaster who emigrated from Barbados to St. Vincent with his wife, Millicent, around the turn of the century and placed great expectations of scholastic excellence on his four daughters and four sons. His second son, known as Cuthbert, was Walker's father. Cuthbert came to New York to study at City College and work for the Erie Railroad. When the Depression struck and the railroad's headquarters relocated to Cleveland, Cuthbert moved with his job. In Cleveland, he attended John Marshall Law School and met his future wife.

Local star makes good. Walker's techniques produced this image of the Sun, which lit up the Sept. 30, 1988, cover of Science magazine.
Reprinted with permission from Science magazine, copyright 1988 American Association for the Advancement of Science.*

Walker's maternal grandfather, Ormand Forte, emigrated from Barbados to the United States with his wife, Ida. He attended Macalester College in St. Paul and worked for Hanna Steel in Cleveland, where he attracted the interest of steel magnate Mark Hanna, who supported his aspiration to set up an African American newspaper in Cleveland. Walker's mother, Hilda, was born in 1911, four years before her father launched his first newspaper, The Advocate, which grew in influence and spawned three other papers.

Arthur Walker was born in Cleveland on Aug. 24, 1936. He was an only child but was close to his many cousins. In 1941 the family moved to New York, where Walker's father set up his own law practice.

From an early age, Arthur loved science. Hilda and Cuthbert both sought to provide the best for their son, but it was Hilda who played a pivotal role in making sure young Art had the opportunities to pursue the kind of career that he wanted.

When his elementary school in New York's Sugar Hill area had an absentee problem -- with its teachers -- Hilda Walker organized the other parents to stand at various locations of the school and record the comings and goings of teachers ditching class to run errands. When the parents presented these data to the authorities, the officials solved their problem by transferring young Arthur -- and therefore Hilda -- to a school outside their district.

In his new school, Walker discovered the library and the world of science. To study the universe like Albert Einstein became his goal -- so much so that his mother encouraged him to take the test for the Bronx High School of Science.

"He developed a keen interest in chemistry there," said Stanford's Thomas. "But his chemistry teacher was worried about the job prospects in the U.S.A. for a black chemist, suggesting that maybe he would have better luck in Cuba." When that teacher tried to steer Walker away from physics as well, Hilda paid a visit to the school and told him "in no uncertain terms" that her son would study whatever he wished, said Walker's cousin Asquith Phills, an Exxon executive.

Walker decided to pursue physics, and his mother encouraged him to apply to the Case Institute of Technology in Cleveland. He received his baccalaureate in physics with honors in 1957. At the University of Illinois, he earned his master's degree in 1958 and doctorate in 1962 with a dissertation on the use of radiation to produce the particles that bind protons and neutrons together in the atomic nucleus.

Walker joined the U.S. Air Force in 1962 as a first lieutenant and was assigned to the Air Force Weapons Laboratory, where he developed instrumentation for an experiment that involved rocket launch of a satellite to measure Van Allen belt radiation in the Earth's magnetic field. This radiation affects satellite operation. Walker said this work ignited his interest in research carried out with space techniques.

Upon completing his military duty in 1965, he joined the Space Physics Laboratory of The Aerospace Corporation, where for nine years he conducted pioneering physics experiments to study the Sun and upper atmosphere of the Earth.

Helping black faculty and students shine

In 1973, the year before he joined Stanford, Walker was offered a professorship at another top research university. "I decided not to accept that one," he recalled. "I remember when I went to visit that institution, the president said, 'We have one Chicano faculty member here on our campus, and if you come and join us, you'll be the first African American faculty member on our campus.' I said, 'That's kind of interesting, but I'm not sure that's exactly what I want.'"

Peter Sturrock, now a Stanford professor emeritus of applied physics, and Arthur Bienenstock, now associate director of the Stanford Linear Accelerator Center, asked Walker to visit Stanford, where he met with Halsey Royden, dean of the School of Humanities and Sciences, and Jim Gibbs, dean of undergraduate studies.

"They said to me, 'We think we have here at Stanford the most distinguished African American faculty of any major research university, and we hope you'll come and join us.' And I said, 'Now that's the kind of attitude I want to see at the university I join.'"

Underrepresented academics have long been placed in the difficult position of splitting their time between activities necessary to achieve tenure and serving as committee members or mentors to boost the number of underrepresented students.

Somehow Walker survived this Catch-22. "Art Walker has been an inspiration to so many faculty here at Stanford, particularly young black faculty," political science Professor Condoleezza Rice said in an interview. "I count myself among the many former assistant professors who looked up to him as someone who was proof positive that promotion and advancement were possible at Stanford if you successfully combined research and teaching."

Walker has served on the African and Afro-American Studies program advisory committee longer than any other member, said program director John Rickford, who holds the Martin Luther King Jr. Centennial Professorship.

"Not as well known is the fact that he's very active on behalf of the African American faculty," Rickford said. "There's no formal black faculty association, but for many years Art served as its informal president."

Walker called this informal association "The Banneker Group" after the first African American man of science, Benjamin Banneker (1731-1806). A free man, Banneker was largely self-educated and owned a farm near Baltimore. In 1761, he built a wooden clock that kept precise time; he accurately predicted a solar eclipse in 1789 and published almanacs from 1791 to 1802. He sent a copy of his first almanac to Thomas Jefferson, then secretary of state, with a letter asking Jefferson's aid in bringing about better conditions for American blacks. Jefferson shared the almanac with European scientists, who praised its accuracy.

Banneker also wrote poetically about stars and other celestial bodies, and Walker would share this poetry with faculty who gathered at a telescope on a hill to view a heavenly event. Rickford said the poetry gave him "a sense of the joy that Art feels when he looks at the stars."

The Banneker Group pushed for more black faculty, for the African and Afro-American Studies program to have its own billets and for a research institute to study race and ethnicity.

"All of us benefited from Art's activities on our behalf and were in turn grateful for them," Rickford said. "His involvement was all the more remarkable because he didn't come from African American literature or African American history or sociology or anthropology, or any of the many fields that normally intersect in a very natural way with African and Afro-American Studies. Here was a person who was doing this with no political or professional advantage of his own to be gained. It was purely his concern for the larger issues that were involved."

Superstars under pressure

"Stanford's physics community is the most exciting place in the world to do physics," said Walker, who has students and colleagues in the departments of Physics, Applied Physics, Electrical Engineering, Materials Science and Mechanical Engineering, as well as at the Stanford Linear Accelerator Center. "It's wonderful to walk down the hall in the physics building. If you're not careful, you'll stumble across a Nobel Prize winner who's doing something extremely exciting, inventing something that you may yourself be able to use in your own research."

But being part of Stanford's star-studded physics community is not just about research. It's about people. And people, with their egos and agendas and opinions, are not as easy as protons.

Nobel Prize-winner Professor Steve Chu said he appreciates going into the astronomer's office to "chit-chat about everything," including waxing and waning stresses in the department: "He'd just say, 'Well, let's figure this out,' and tell me what he thought. He was in fact the Physics Department ombudsman. . . . Art saw right through all the clutter of what was going on and had very wise and soothing things to say."

Clutter is something Walker is used to, colleagues teased. Every horizontal surface in the astronomer's office is piled high with reprints and manuscripts. Chu presented Walker with a book about Superman at the tribute. Its inscription read: "To Art, for your X-ray-like ability to see through all the clutter and arrive at the core of a difficult problem; for your soothing counsel to students and faculty and in championing truth and justice, which is not exclusive to the American way; for your rocket-borne experiments that have leapt over tall buildings in a single bound, I give you this book of one of my childhood heroes, of which there is a bit in common."

Called to serve

Public service on the part of scientists is crucial to the federal government, as Congress uses committee advice almost like a blueprint to see that federal agencies are following the recommendations of the scientific community. Throughout his career, Walker has led or served on innumerable NASA, National Science Foundation and National Academy of Sciences committees.

Walker's committee service helped build America's network of astronomical observatories. He played the title role in the Walker Committee, which recommended that the national observatories take over the Sacramento Peak Solar Observatory when its Air Force funding was cut. "[That change] gave us the critical mass so that we can truly say that we have a national solar observatory," said Sydney Wolff, director of the National Optical Astronomy Observatories.

In 1986, President Ronald Reagan called Walker to serve on one of the most important committees in U.S. history -- the commission investigating the space shuttle Challenger explosion. The 13 commission members, chosen for their professional expertise in engineering, industry, law, science and flying, included Apollo 11 commander Neil Armstrong, former Secretary of State William Rogers, Nobel Prize-winning physicist Richard Feynman and Walker's former student, astronaut Sally Ride.

"The Challenger accident occurred something like the 25th space shuttle mission in," said NASA's Wagner. "We're now, as a result of the Challenger Commission and Art's work, getting NASA back into space with the shuttle. We're now about to launch the 100th space shuttle, so there were definitely things done right."

Never the same space twice

As the human race pushes the envelope of the known universe, technology developed by Walker and others will continue to be its collective eyes. Walker's X-ray images revealed a new face of the Sun.

And as technology evolves, the next generation will see something new, too. Walker and Cabrera have just begun a collaboration to use X-ray spectroscopy to create colorful 3-D images that reveal the compositions of celestial bodies.

Said Walker: "I truly believe that if we are successful, this will revolutionize X-ray spectroscopy, bring X-ray spectroscopy and X-ray observations to the same level as optical observations in astronomy and really revolutionize our understanding of the universe."

*** The image of the Science magazine cover is reprinted with permission from Science magazine, copyright 1988 American Association for the Advancement of Science. Readers may view, browse and/or download material for temporary copying purposes only provided these uses are for non-commercial personal purposes. Except as provided by law, material may not be further reproduced, distributed, transmitted, modified, adopted, performed, displayed, published, or sold in whole or in part, without prior written permission from the publisher.

The Transition Region and Coronal Explorer (TRACE) satellite, developed by the Stanford-Lockheed Institute for Space Research, shows convection and other activity in the corona. Such images may help scientists solve a solar mystery: Why is the Sun's upper atmosphere hotter than its surface?
Film courtesy TRACE