Florida's first same-sex weddings take place after a judge's ruling that a gay marriage ban is unconstitutional takes effect. (Reuters)

Gay couples began marrying in Miami on Monday, kicking off a pivotal week when the Supreme Court will have a chance to consider whether same-sex couples have a constitutional right to marry or whether states may limit marriage to a man and a woman.

A Miami-Dade County judge gave couples there a head start before marriages begin elsewhere Tuesday in the nation’s third-most-populous state. With the addition of Florida, more than 70 percent of Americans now live in the 36 states and the District of Columbia where same-sex marriages are allowed, according to estimates by the Williams Institute at the UCLA School of Law.

On Friday, Supreme Court justices will meet in private to consider whether to act on cases that could provide a nationwide answer on whether same-sex marriages must be allowed. On the same day, a federal appeals court will consider bans in Texas, Mississippi and Louisiana.

“It’s an incredible confluence of events,” said Shannon Minter, legal director for the National Center for Lesbian Rights. “It’s the culmination of many years of work.”

The marriages in Florida and the potential for a constitutional decision by the Supreme Court this year reflect the rapid advance of the same-sex-marriage movement and a remarkable change in public opinion. When the court heard oral arguments about California’s Proposition 8 and the federal Defense of Marriage Act (DOMA) in 2013, only nine states and the District allowed such unions.

The justices this week will be considering petitions from five states where lower-court judges, bucking a nationwide trend, upheld laws banning same-sex marriage and barring the recognition of such unions performed in states where they are legal.

In all but one case, even the winning side has asked the Supreme Court to accept the cases and settle the issue during its current term, which will conclude at the end of June.

Without explanation, the justices in October passed up that chance. But that was before a panel of the U.S. Court of Appeals for the 6th Circuit in Cincinnati ruled that there was no constitutional right to marriage that must be extended to gay couples and that states were free to define marriage as they wished.

Because four other regional appeals courts have ruled the other way, “the court is more likely to decide the issue now than when it denied review last October,” Kyle Duncan, a Washington lawyer defending Louisiana’s bans, said in an e-mail.

The Supreme Court does not have to announce its decision on the petitions Friday. But generally the justices must accept a case by the end of January in order to hold oral arguments and rule by June.

If they do not, same-sex marriages will probably remain legal in the majority of states through 2015 and banned in the rest.

The growth in the availability of same-sex marriage is a result of a nearly unanimous string of federal court decisions following the twin gay rights victories the Supreme Court delivered in 2013.

Since then, the court has repeatedly rebuffed states asking that they not be forced to follow the lower-court rulings and offer marriage licenses until the constitutional question is settled.

In Florida’s case, for instance, the justices refused — over the objections of Justices Antonin Scalia and Clarence Thomas — to extend a stay, even though the issue was on appeal. A federal judge’s order ruling the state’s ban unconstitutional has not yet been reviewed by the next court up the ladder, the U.S. Court of Appeals for the 11th Circuit.

To some court-watchers, that refusal was evidence that the five-justice majority that struck down part of DOMA — a section that withheld federal recognition of same-sex marriages performed where they are legal — is prepared to take the next step.

The justices are no doubt aware that thousands of marriages have resulted from their actions. There is some dispute about what would become of those unions should the Supreme Court rule against same-sex-marriage proponents.

But Evan Wolfson, president of the group Freedom to Marry, says none of the marriages would be in jeopardy.

“Couples who get legally married will remain legally married — as married as any couples on the planet — even in the unlikely event that the Supreme Court were to later rule there is no constitutional right going forward,” Wolfson said in a statement.

Duncan said it is impossible to predict how the court will rule on same-sex marriage based on its record in considering stays. Early on, for instance, the court granted Utah’s request for a stay and stopped the marriages that were being performed there.

But ultimately, the court decided not to review lower courts’ decisions, and same-sex marriages resumed in Utah.

“All we can say concretely is that the Supreme Court has not yet rendered a single substantive decision on state marriage laws,” Duncan said.

The growth in the number of states offering same-sex marriage since 2013 has been almost entirely a result of legal challenges. Most — but not all — states vigorously defended their laws and voters’ decisions to limit marriage to its traditional definition.

Former Florida governor and likely presidential candidate Jeb Bush noted that in a recent interview with the Miami Herald.

“It ought to be a local decision. I mean, a state decision,” Bush said. “The state decided. The people of the state decided. But it’s been overturned by the courts, I guess.”

On Monday, as the marriages began, Bush offered a more conciliatory take. He asked for “respect for the good people on all sides of the gay and lesbian marriage issue — including couples making lifetime commitments to each other who are seeking greater legal protections and those of us who believe marriage is a sacrament and want to safeguard religious liberty.”

In Florida, various plaintiffs filed several lawsuits in state and federal courts, and they were victorious in each. Most significant was a decision by U.S. District Judge Robert Hinkle of Tallahassee, who ruled the ban unconstitutional.

But there was confusion about whether Hinkle’s decision affected all 67 Florida counties or just the one where the case was brought. Hinkle issued an unusual clarification on New Year’s Day saying all county clerks should prepare to issue marriage licenses.

“History records no shortage of instances when state officials defied federal court orders on issues of federal constitutional law,” Hinkle wrote. “Happily, there are many more instances when responsible officials followed the law, like it or not.”

Hinkle had stayed his order at the time of his original decision but said it would expire at midnight Monday. It is that stay that the 11th Circuit and then the Supreme Court refused to extend.

Proponents of same-sex marriage went to state court Monday and convinced Circuit Judge Sarah Zabel to lift the stay immediately.

“In the big picture, does it really matter whether or not I lift the stay or leave it until tomorrow?” Zabel said from the bench, according to the Miami Herald. “I’m lifting the stay.”

Zabel then performed marriage ceremonies for two of the couples who had been plaintiffs in the case.