Intermittent spurts of rainfall shortened but could not stop Yale’s 311th Commencement exercises, which brought the College and the University’s graduate and professional schools to Old Campus on Monday.

In front of a crowd of nearly 18,000, the University conferred 3,021 degrees — 1,249 to undergraduates — and awarded another 285 provisionally to students in the Law School and in the School of Medicine’s Physician Assistant Program, who have not yet completed their courses of study. Provost Peter Salovey also announced the recipients of nine honorary doctorates, including former U.S. Secretary of Defense Robert Gates and former chief justice of the Supreme Judicial Court of Massachusetts Margaret Marshall LAW ’76.

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As students marched onto Old Campus around 10:30 a.m., rain started to fall, sending members of the audience into a momentary panic as they scrambled for umbrellas. Because of the weather, student marshals representing the degree recipients did not come to the stage, the undergraduate prize winners announced on Class Day were not introduced again and the first hymn on the program was omitted.

The crowd turned into a sea of blue as students and spectators donned blue ponchos supplied by the University. Officials manning information booths said they ran out of ponchos shortly after the first spurt of rain.

But the weather did not dampen the mood of graduates, who marched into Old Campus through Phelps Gate, Miller Gate and the High Street Gate behind a marching band, flags carried by student award winners and marshals carrying heavy University maces.

Following tradition, Sunday’s Class Day brought out hats of myriad color and variety, including a “solar system-themed” hat, a “thinking cap” and a recycling bin filled with cans. Students toned down the attire for Commencement, though many graduates had text and colorful symbolism on their mortarboards and accessorized according to their Yale affiliations.

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Fifteen actors and actresses graduating from the School of Drama wore red noses along with their graduation attire. After the ceremonies, they said the decoration expressed their “love of clowns.” Meanwhile, graduates from the School of Public Health put slogans such as “I Stand for Women’s Health” on their mortarboards.

The ceremony began with Yale College Dean Mary Miller, who presented undergraduate candidates for degrees.

At the Class Day festivities, Miller asked students to “literally explode” when she asked University President Richard Levin to confer degrees on them the following day. The class of 2012 responded to her request on Monday with rambunctious cheering.

After Miller, the deans of each school presented their candidates for degrees to Levin, taking care to note candidates whose degrees are still provisional: law students have yet to take their final examinations, while students in the Physician Assistant program will not complete their degrees until December.

Once graduates had been presented for their degrees, Levin presented honorary doctoral degrees to nine individuals in fields ranging from environmental science to music. He told graduating students that these honorees should “serve as examples to you…to value those elements of the human character that they embody: creativity, curiosity, integrity.”

Robert Gates, who served as director of the Central Intelligence Agency from 1991 to 1993 and as U.S. secretary of defense from 2006 to 2011, was awarded a doctorate of humane letters by the University. Levin hailed him as “a true American patriot,” adding that as secretary of defense Gates “called attention to the twin goals of protection and peace even in the midst of two wars.”

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Two of the honorary doctorate recipients — Aaron T. Beck MED ’46 and Margaret Marshall — were receiving a degree from Yale a second time. Beck, who pioneered the use of cognitive behavioral therapy to treat mental illness such as depression, was awarded a doctorate of medical sciences. Marshall, who in addition to her work on the Supreme Judicial Court of Massachusetts is a former Yale Corporation fellow, was honored with a doctorate of laws.

“You have devoted your life to the pursuit of justice, from your native South Africa as a student protesting apartheid to the Supreme Judicial Court of Massachusetts, as the first woman to serve as its chief justice,” Levin said in his citation for Marshall. “You changed the legal landscape with your courageous decision to recognize the right of same-sex couples to marry,” he continued, eliciting loud cheers from the assembled crowd.

An honorary doctorate of humanities went to Robert Darnton, a cultural historian who specializes in the history of the book, while a doctorate of science went to environmental scientist Jane Lubchenco. Levin called Lubchenco a “steward of sky and sea” for her work leading the National Oceanic and Atmospheric Administration and founding organizations to communicate scientific findings to the public.

Angelika Neuwirth received a doctorate of divinity for her scholarship on the Qur’an, and violinist Midori was awarded a doctorate of music for both her musical talents and philanthropic ventures, which Levin said had an impact “far beyond the concert hall.” Midori is the founder of Midori & Friends, a nonprofit organization that provides musical instruction to 15,000 students a year in New York City.

Sociologist William Julius Wilson received a doctorate of social science for his research on race, poverty and inequality, while U.S. poet laureate Richard Wilbur received a doctorate of letters for his poetry and literary translation.

Outside Old Campus, half a dozen individuals held wooden signs pointing out U.S. income inequality and rising student debt. Interviewed after the Commencement ceremony, the group said they were not protesting so much as recognizing that it was the “students’ day.”

“Graduation from Yale is a powerful thing,” one member said. “People respect the degree and students should recognize they are in the position to change the world.”

Diploma ceremonies in each of the residential colleges that take place after the Old Campus ceremony were moved to their alternate locations due to the rain.