April Fools' Day, or All Fools' Day, though not a holiday in its own right, is a notable day celebrated in many countries on April 1. The day is marked by the commission of hoaxes and other practical jokes of varying sophistication on friends, enemies and neighbors, or sending them on fools' errands, the aim of which is to embarrass the gullible.
The origins of this custom are complex and a matter of much debate. It is likely a relic of the once common festivities held on the vernal equinox, which began on the 25th of March, old New Year's Day, and ended on the 2nd of April.
Though the 1st of April appears to have been observed as a general festival in Great Britain in antiquity, it was apparently not until the beginning of the 18th century that the making of April-fools was a common custom. In Scotland the custom was known as "hunting the gowk," i.e. the cuckoo, and April-fools were "April-gowks," the cuckoo being a term of contempt, as it is in many countries.
Europe may have derived its April-fooling from the French. French and Dutch references from 1508 and 1539, respectively ,describe April Fools' Day jokes and the custom of making them on the first of April. France was one of the first nations to make Jan. 1 officially New Year's Day (which was already celebrated by many), by decree of Charles IX. This was in 1564, even before the 1582 adoption of the Gregorian calendar (See Julian start of the year). Thus the New Year's gifts and visits of felicitation, which had been the feature of the 1st of April became associated with the first day of January, and those who disliked or did not hear about the change were fair game for those wits who amused themselves by sending mock presents and paying calls of pretended ceremony on the 1st of April. In France the person fooled is known as poisson d'avril (April fish). This has been explained as arising from the fact that in April the sun quits the zodiacal sign of the fish. The French traditionally celebrated this holiday by placing dead fish on the backs of friends. Today, real fish have been replaced with sticky, fish-shaped paper cut-outs that children try to sneak onto the back of their friends' shirts. Candy shops and bakeries also offer fish-shaped sweets for the holiday.
Alabama changes the value of pi: The April 1998 newsletter of New Mexicans for Science and Reason contained an article written by physicist Mark Boslough claiming that the Alabama Legislature had voted to change the value of the mathematical constant pi to the "Biblical value" of 3.0. This claim originally appeared as a news story in the 1961 science fiction novel "Stranger in a Strange Land" by Robert A. Heinlein.
Spaghetti trees: The BBC television program "Panorama" ran a famous hoax in 1957, showing the Swiss harvesting spaghetti from trees. They had claimed that the despised pest the spaghetti weevil had been eradicated. A large number of people contacted the BBC wanting to know how to cultivate their own spaghetti trees. It was in fact filmed in St Albans.
Left-handed Whoppers: In 1998, Burger King ran an ad in USA Today, saying that people could get a Whopper for left-handed people whose condiments were designed to drip out of the right side. Not only did customers order the new burgers, but some specifically requested the "old," right-handed burger.
Taco Liberty Bell: In 1996, Taco Bell took out a full-page advertisement in The New York Times announcing that they had purchased the Liberty Bell to "reduce the country's debt" and renamed it the "Taco Liberty Bell." When asked about the sale, White House press secretary Mike McCurry replied tongue-in-cheek that the Lincoln Memorial had also been sold and would henceforth be known as the Ford Lincoln Mercury Memorial.
San Serriffe: The Guardian printed a supplement in 1977 praising this fictional resort, its two main islands (Upper Caisse and Lower Caisse), its capital (Bodoni), and its leader (General Pica). Intrigued readers were later disappointed to learn that San Serriffe (sans serif) did not exist except as references to typeface terminology. (This comes from a Jorge Luis Borges story.)
Metric time: Repeated several times in various countries, this hoax involves claiming that the time system will be changed to one in which units of time are based on powers of 10.
Smell-o-vision: In 1965, the BBC purported to conduct a trial of a new technology allowing the transmission of odor over the airwaves to all viewers. Many viewers reportedly contacted the BBC to report the trial's success. This hoax was also conducted by the Seven Network in Australia in 2005. In 2007, the BBC website repeated an online version of the hoax.
Tower of Pisa: The Dutch television news reported once in the 1950s that the Tower of Pisa had fallen over. Many shocked people contacted the station.
" Source: Wikipedia