150th anniversary for London's famous clock
The clock began keeping time on May 31, 1859, and the bell was struck for the first time six weeks later on July 11.
The name is commonly used to describe the clock tower, including the clock face and the bell. But technically, Big Ben refers just to the biggest of the bells inside the tower — the Great Bell — which weighs nearly 12 tonnes.
No special events were planned to mark the anniversary, aside from an exhibition at Portcullis House, the nearby parliamentary office complex, due to open Sept. 19.
Security measures mean few are granted admission to the clock tower, and there's no elevator, so those who are escorted in must climb 334 winding limestone stairs.
The city's most famous landmark is 95.7 metres high, or roughly 16 storeys.
The chimes, supposedly based on four notes from Handel's "Messiah," ring out every quarter-hour from the intricately ornamented belfry. The bongs of Big Ben itself are heard every hour.
Low-tech yet accurate
The five-tonne clock mechanism, like a giant wristwatch, is wound three times a week. In the age of atomic clocks, its near-perfect time is regulated by heavy old pennies laid on or removed from the pendulum.
Big Ben mechanic Ian Westworth says the bell has a crack in two places, which gives it a slightly off-pitch sound when struck.
He says there are a couple of interesting stories about how it was given its nickname, but many think it was named after Sir Benjamin Hall, the commissioner of works at the Palace of Westminster during the time of the clock tower's construction.
Westworth says Hall's physique was described as bell-shaped.
With files from The Associated Press