After months of waiting, today is US election day.

Here, Owen Amos outlines somethings you need to know – and many more you don’t…

SOME THINGS YOU NEED TO KNOW...

US citizens do not vote for the president. Instead, they vote for electors, who pledge to support a party’s candidate. A state’s number of electors depends on its size – for example, Delaware has three, while California has 55.

In all but two states (Maine and Nebraska), the winner takes it all – whichever party wins most votes wins the support of all the electors. So, if 51 per cent of Californians votes for Barack Obama and 49 per cent for John McCain, all 55 electors would support Obama.

There are 538 electors in the US Electoral College. To win, a candidate needs the support of a majority – 270. Should no candidate win a majority, the decisions is passed to the House of Representatives. The Electoral College cast their votes – though the result, of course, is already known – on December 15, and the president will be inaugurated on January 20, 2009.

AND SOME THINGS YOU DON’T

At William Hill, Barack Obama is 1/14 to win the election. John McCain is 13/2.

Obama is 6ft 1ins. McCain is 5ft 6ins. In the last 20 elections, the taller man has won 15 times. But George W Bush, at 5ft 11ins, was shorter than both his opponents – John Kerry was 6ft 4ins, and Al Gore was 6ft.

If McCain wins, he would be the second shortest president in history, after 5ft 4ins James Madison, the fourth president.

William Taft, the 27th president, was the heaviest, at around 21 stones.

Virginia, the 37th largest state, has been birthplace to eight presidents – more than any other. Their most recent was Woodrow Wilson, the 28th president. Nearby Ohio has been birthplace to seven presidents.

Alaska, the largest state, has had no presidents, Texas, the second largest, has had two, and California, the third largest, one.

Neither candidate was born on the US mainland. Obama was born in Honolulu, Hawaii, McCain in Coco Solo US Naval Air Station, Panama.

Obama is senator of Illinois, where he moved in 1985 to work for a church-based community organisation. McCain is senator of Arizona, where he moved in 1981 after retiring from the navy.

The US president is paid $400,000 a year, slightly more than our prime minister, on £189,994.

In Article Two, Section One of the US Constitution, it says: “No person except a natural born citizen, or a citizen of the United States, at the time of the adoption of this constitution, shall be eligible to the Office of President.” However, “citizen” can include someone born outside the US with a citizen as parent.

Martin Van Buren, the eighth president, was the first president born in the US – that is, the first born after the signing of the Declaration of Independence. He was born December 5, 1782.

Article Two of the constitution, outlining the rights and responsibilities of the president, is just 1,054 words long.

The constitution states the president must be at least 35 and have been a US resident for 14 years. Obama is 47, McCain is 72, and would become the oldest US president at inauguration. Ronald Reagan, who was 69, holds the record.

If the president dies, the vice president takes office. If both die at the same time, the speaker of the house, currently Nancy Pelosi, a Democrat, becomes president.

Obama or McCain will be the 44th president.

Eight have died in office, including four who were assassinated – Abraham Lincoln, James Garfield, William McKinley and John F Kennedy.

From William Harrison, in 1840, to John F Kennedy, in 1960, all seven US presidents elected in a year ending in 0 died in office.

Ronald Reagan, elected in 1980, broke this chain, known as the Curse of Tippecanoe.

Just 69 days into his presidency, though, Reagan survived an assassination attempt.

Of the first five presidents, three – John Adamson, Thomas Jefferson and James Monroe – died on July 4, Independence Day.

McCain would be the fifth president called John, after Adams, Adams, Tyler, and Kennedy. He would be the second McPresident, after McKinley.

Obama would be the first president with a surname beginning with O.

McCain’s middle name is Sidney. Obama’s is Hussein, which some commentators have used as a slur.

Both Obama and McCain are left-handed.

This means that, since and including Reagan, four of the next five presidents will have been left-handed. Only George W Bush was right-handed.

As well as Obama and McCain, there are four other candidates on enough state ballots to theoretically become president. Chuck Baldwin, a 56-year-old pastor and radio show host, is standing for the Constitution Party, which supports reduced bureaucracy, reduced public spending, and noninterventionism abroad.

Cynthia McKinney, a 53-year-old former Democratic congresswoman and college professor, is standing for the Green Party.

Bob Barr, a 59-year-old former Republican congressman and US attorney, is standing for the Libertarian Party, which supports laissez-faire markets and noninterventionism abroad.

Ralph Nader, 74, an independent, is standing for the fourth time. In 1996 and 2000 he stood for the Green Party and in 2000 was accused of taking crucial votes from Al Gore.

In 2000, Ralph Nader won 2,882,955 votes, or 2.7 per cent of the vote. In 1992, Ross Perot won 18.9 per cent – the highest third party vote since 1912 – but the electoral college system meant he won no electors.

Turnout for today’s election is expected to be the highest since 1960 – Kennedy v Nixon – when it was 63.1 per cent. In 2004, it was 56.7 per cent, up from 51.1 in 2000.