Gun salutes rang out in Hyde Park on Tuesday to mark Queen Elizabeth II's 89th birthday.
A 41-gun salute was fired at midday in Hyde Park, with a 62-gun salute following from the Tower of London—and it could happen all over again within days to celebrate the birth of Prince William and his wife Kate's second baby.
Gun salutes are customarily fired, both on shore and at sea, as a sign of respect or welcome.
Just as a salute with the open hand was used historically to show that no weapon was concealed in the palm, so the firing of cannon as a salute indicated the friendly intent of an empty chamber.
The basic Royal salute is 21 rounds. In Hyde Park an extra 20 rounds are added because it is a Royal Park.
At the Tower of London 62 rounds are fired on Royal anniversaries (the basic 21, plus a further 20 because the Tower is a Royal Palace and Fortress, plus another 21 'for the City of London') and 41 on other occasions.
The Tower of London probably holds the record for the most rounds fired in a single salute: 124 are fired on 10 June when The Queen's official birthday (62 rounds) coincides with The Duke of Edinburgh's birthday (also 62 rounds).