One of my favorite entertainments on British television is the programme University Challenge, a British version of College Bowl in which teams from two universities compete to answer questions posed by prickly host Jeremy Paxman. The questions often require the teams to make complex mathematical calculations in their heads, or identify songs associated with various football teams, or know which former Prime Minister was created Baron of Bedwelty. One question which completely stumped both teams—a rare occurrence—was, "How many years are marked by a sesquicentennial?"
In England, apparently, few things as young as 150 are worthy of being celebrated. But in America, sesquicentennials are happening all the time. I celebrated my first sesquicentennial in in my freshman year in college (1982-1983), when Oberlin College celebrated the 150th anniversary of its founding. In Minnesota, we are now experiencing a rash of sesquicentennials: the University of Minnesota (2001), Hamline University (2004), the city of Northfield (2005), the First United Church of Christ, Northfield (2006), Minnesota statehood (2008).
Yesterday, Boxing Day, was the quadricentennial (400 years) of the premier of Shakespeare's King Lear, first performed for King James I at Whitehall Palace on December 26, 1606.
Etymological note. Sesqui- comes from the Latin semis (a half) + -que (and), so a sesquicentennial is "a centennial and a half" (or, 150 years).