Why did Samoa skip a whole day in 2011?

Samoa skipped a day to move to the other side of the International Date Line. That line, running through the Pacific from pole to pole, is where one calendar day turns into the next. Since 1892, Samoa had been on the American side, but by 2011 its biggest trading partners were Australia and New Zealand, on the other side. Being 21 hours behind them meant their weekends fell on different days, leaving only four shared workdays a week. So Samoa removed Friday 30 December 2011 from its calendar and jumped to their side of the line.

That is also why the date line zigzags. It roughly follows the 180° meridian, but it bends around islands so that neighbours who trade together can share the same date. Kiribati, whose islands once straddled the line, had the same problem: its two halves only had four weekdays in common. In 1994 its eastern islands deleted Saturday 31 December, and the line now swings far east to go around the whole country. As a bonus, Kiribati's Line Islands were the first place on Earth to see the year 2000.

Samoa had already changed sides once. In 1892, American traders persuaded its king to switch to the American date, which was done by living Monday 4 July twice. Today the line runs between Samoa and American Samoa, so neighbouring islands live a day apart.