Residents of Lerwick, Shetland, carry a Viking longship through the streets.Image © Jeff Mitchell/Getty Images 2006
Scotland was long under the influence of Viking culture, in fact it was part of Norway for some 5 centuries. Much later on the soldiers and sailors returning from the Napoleonic Wars, who had learned to enjoy a week long season of partying after Christmas was over, their partying usually included plenty of setting things on fire, including inflaming barrels of tar. Which often exploded. the resulting death and destruction, sorta put a damper on things.
But, have no fear! in the 1870's a group of enterprising young folks decided to organise the festivities and thus make them a bit safer, and I would guess keep the complaints to a minimum, and a bit more fun, they moved the Festivities to the last Tuesday of Jan. They added a torchlight parade, and a decade later, the Viking theme was added, and the burning of a longship became a part of the celebrations.
There is also much feasting and drinking, singing and dancing. to learn more about Up Helly Aa click on the official site at http://www.uphellyaa.org/.