At about 12:30PM NYC-time today, Queen Elizabeth will become longest ruling monarch in British history. The BBC runs the numbers:
The Queen will have reigned for 63 years and seven months – calculated at 23,226 days, 16 hours and approximately 30 minutes at about 17:30 BST. Prime Minister David Cameron will lead tributes in the House of Commons and there will be a River Thames salute. The Queen, who is 89, will spend the day on official duties in Scotland. The exact moment the Queen reaches the milestone is not known because her father, George VI, passed away in the early hours of 6 February 1952. Business in the Commons will be postponed for half an hour so MPs can pay tribute to the Queen. On the Thames, a flotilla of historic vessels, leisure cruisers and passenger boats will take part in a procession between Tower Bridge and the Houses of Parliament. The bridge will lift as a sign of respect and HMS Belfast will sound a four-gun salute. The BT Tower in central London will scroll the message “long may she reign”.
The record was previously held by Queen Victoria, who ruled from 1837 to 1901. Wikipedia maintains an interesting longevity list broken down by England, Scotland, Wales, Great Britain, and the United Kingdom overall. The shortest rule goes to England’s Lady Jane Grey, aka the “Nine Day Queen.”