Scots decide today whether to end 300 years of union with Great Britain and go it alone as they cast ballots in a historic referendum that is sure to have a lasting impact no matter the outcome.

Public opinion polls in recent days have suggested that Scotland is evenly split on the question and that the vote could be extremely close. The options are to vote "yes" or "no" to the question: "Should Scotland be an independent country?"

The results are expected on Friday.

The BBC says:

"With 4,285,323 people — 97% of the electorate — registered to vote, a historically high turnout is expected."Votes will be cast at 2,608 polling places across the country until 22:00 on Thursday. The result is expected early on Friday morning."

As NPR's Ari Shapiro reports from Edinburgh, British Prime Minister David Cameron made one final emotional appeal to keep the United Kingdom intact.

Speaking in Aberdeen, Cameron warned that a vote for independence would precipitate a "painful divorce." In the past he said that a decision by Scots to leave the union would leave him heartbroken.

Acknowledging the unpopularity of his conservative government among more liberal-minded Scots, Cameron said bluntly: "If you don't like me — I won't be here forever. But if you leave the U.K., that will be forever."

(The Two-Way's Krishnadev Calamur has a look here at some of the headlines from U.K. newspapers about the referendum.)

President Obama also weighed in on the referendum just 24 hours before the voting began, saying he'd like to see the United Kingdom remain "strong, robust and united." Former President Bill Clinton also urged a "no" vote.

Alex Salmond, the leader of the campaign for independence, cast his ballot in his home village of Aberdeenshire.

"I got a fantastic night's sleep. Obviously there's a great deal of anticipation, it's a once-in-a-lifetime opportunity, it's a day that everybody will remember," he said.

"We're in the hands of the people of Scotland, and there's no safer place to be than in the hands of the Scottish people," Salmond said.

Leighton Andrews, the public services minister for Wales, told the BBC last week that he believed that "radical" constitutional change was in store for the U.K. as a direct result of the vote.

"I think it will have major implications for the U.K. regardless of the result of the referendum," he said.

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