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With that momentum behind them, they will head to the Supreme Court in March for a case regarding California's ban on same-sex marriage. The case asks a very broad question: Do same-sex couples have a fundamental right to marry under the U.S. Constitution? But there are a number of ways the court could rule in favor of gay rights, without reaching that big question.

Gay advocates want a win. But some would be satisfied with a narrow victory that would continue the momentum and allow them to work on the state level to get more states on board, before perhaps returning to the Supreme Court.

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In a recent piece on Scotusblog, Kenji Yoshino, a professor at New York University School of Law, explains ways that the court could hand a victory to gay-rights advocates, yet stop short of a ruling that would affect all 50 states.

One such ruling would focus on the "lack of justification for giving same-sex couples all the rights and responsibilities of marriage but withholding the word 'marriage' from them." The ruling would affect only a few other states, including California.

Without even the tea leaves of oral arguments, it's far too early to guess how the court might rule.

But gay-rights advocates hope that if the Supreme Court issues a broad opinion in their case, the 40th anniversary of the ruling will not include large protests in the streets.