Big Ben—which just marked its 150th birthday—is actually the name of the bell, not of the Houses of Parliament's famous clock tower that houses it.
But Big Ben is only a nickname. The bell's official name is "The Great Bell," which is much less distinctive.
For the record, Big Ben is more than 7 feet tall and weighs about 30,000 pounds. And this is what Big Ben sounds like at 12 o'clock:
