"Every drop is a blessing, according to tradition," said Langer. "May you be drenched by rain."
Reframing common events, even rain in darkness, in religious terms is at the essence of Langer's work: trying to bring secular Jews into greater religious practice. Though Chabad Lubavitchers like him occupy a tiny piece of the Jewish diaspora, they have had a pronounced effect on defining Hanukkah in the American public sphere.
And, in many ways, the story of that impact can be told through the menorah in Union Square.
The Bay Area's most public and frenzied shopping mecca is a peculiar place for lighting a menorah, a sacred eight-night event normally reserved for the intimacy of a home. But for Langer, who sees most Jews as having fallen far from true observance, that's the point. He and other Chabadniks, as they are known, are bringing Judaism out to the world - wherever it may be. There are Chabad Houses around the world, including Mumbai, where the rabbi and his wife were killed in the recent terrorist attacks.
At Hanukkah, Langer said, "the marketplace is where Jews are at."
The organizers are among the strictest followers of Jewish law. Langer told the audience that lighting a menorah at night is a metaphor for how simple acts of kindness add light to a dark world. Those acts multiplied, he said, will prompt the resurrection of the messiah, who will unite all Jews and lead them to Israel while also bringing everlasting peace to the world.
The event at Union Square offers a rare glimpse into the breadth of contemporary Jewish identity, particularly its margins.
On Sunday, there were young couples making out in the rain while others danced to the Hasidic rock band, Isaiah and the Prophets, who hail from the center of the Chabad universe, the Crown Heights neighborhood in Brooklyn. Several attendees said the Union Square menorah lighting is the only religious event they'd attend all year.
"I worship the universe," said Nissim Lanyadoo, 59, who was born in Baghdad and moved to Israel and Montreal before settling in Tiburon. He doesn't attend synagogue at all - "it's a long story," he said - but he's been coming to the Union Square menorah lighting for years.
He said of the people gathered, dancing, playing with dreidels and eating latkes: "It's the way it's supposed to be: a joyous occasion."
David Moudgil grew up in a house where his father was Hindu and his mother was Jewish, but the parents didn't want to impose any one religious view. The San Pablo resident is raising his two daughters with the Catholic faith of his wife, but he still wants his children to have some connection to their Jewish roots.
"I just want my kids to learn more and expose them to more so they have more choices as they grow up," said Moudgil, 42.
That many have a peripheral connection to Jewish faith is, for Langer, emblematic of a larger dilemma. A poll conducted by the Pew Forum on Religion and Public Life found that only 16 percent of Jews attend synagogue on a weekly basis.
But Langer said the contrast between his observance and many in the audience doesn't make the public menorah lighting any less important.
"You may never light a menorah again, but for that moment, you're totally immersed in an internal relationship with your maker," he said.
Now in its 34th year, the Union Square menorah lighting was a key to making Hanukkah a well-known holiday, despite its relatively minor role in Judaism. In 1975, Langer, two other Chabad rabbis and rock promoter Bill Graham held the first lighting of a large menorah in Union Square.
It was a concept the Lubavitcher Rebbe, the head of the denomination, saw as an opportunity, given how popular Christmas was in America, said Sue Fishkoff, an Oakland resident and author of the 2003 book, "The Rebbe's Army: Inside the World of Chabad-Lubavitch."
There are now hundreds upon hundreds of menorah lightings across the world, including ones in synagogues not run by Chabadniks. But the Chabad tradition has not been without controversy.
As rain poured on Union Square on Sunday night, Rabbi Yosef Langer called upon those gathered for the lighting of a giant menorah to imagine the cold downpour within the context of Jewish theology.
In 1986, several Jewish organizations and the American Civil Liberties Union sued Chabad and the city of Pittsburgh over that city's public menorah. Jews have often been at the forefront of church-state battles, given their history of being victimized by state-sanctioned religion.
In what has become a landmark case, the court ruled in 1989 in favor of Chabad, saying the menorah was an expression of free speech.
But at the lighting ceremonies, which continue through the week, several see it as an important stand for religious freedom.
Eric Perez, 49, of San Mateo, a rare synagogue attender, says the event protects his religious identity by allowing his faith "to be seen."
E-mail Matthai Kuruvila at firstname.lastname@example.org