The description of Halloween below was harvested from the always excellent Wikipedia's very own Halloween page.
The History of Halloween
Halloween is a tradition celebrated on the night of October 31, most notably by children dressing in costumes and going door-to-door collecting sweets. It is celebrated in parts of the Western world, though most commonly in the United States, Canada, the UK, Ireland, Puerto Rico, and with increasing popularity in Australia and New Zealand. Halloween originated among the Celts in Ireland, Britain and France as the Pagan Celtic harvest festival, Samhain. Irish, Scots, Calan Gaeaf in Welsh and other immigrants brought versions of the traditions to North America in the 19th century. Most other Western countries have embraced Halloween as a part of American pop culture in the late 20th century.
The term Halloween, and its older spelling Hallowe'en, is shortened from All-hallow-even, as it is the evening before "All Hallows' Day" (also known as "All Saints' Day"). In Ireland, the name was All Hallows' Eve (often shortened to Hallow Eve), and though seldom used today, it is still a well-accepted label. The holiday was a day of religious festivities in various northern European Pagan traditions, until Pope Gregory III moved the old Christian feast of All Saints Day to November 1 to give Halloween a Christian interpretation . Halloween is also called Pooky Night in some parts of Ireland, presumably named after the púca, a mischievous spirit.
Halloween is often associated with the occult. Many European cultural traditions hold that Halloween is one of the liminal times of the year when the spiritual world can make contact with the physical world and when magic is most potent (e.g. Catalan mythology about witches, Irish tales of the Sídhe).
Trick or Treat
The main event of modern US-style Halloween is trick-or-treating, in which children dress up in costume disguises and go door-to-door in their neighborhood, ringing each doorbell and yelling "trick or treat!"
In Ireland, great bonfires were lit throughout the breadth of the land. Young children in their guises were gladly received by the neighbors with some "fruit, apples and nuts and of course sweets" for the "Halloween Party", whilst older male siblings played innocent pranks on bewildered victims.
In Scotland, children or guisers are more likely to recite "The sky is blue, the grass is green, may we have our Halloween" instead of "trick or treat!". They visit neighbours in groups and must impress the members of the houses they visit with a song, poem, trick, joke or dance in order to earn their treats. Traditionally, nuts, oranges, apples and dried fruit were offered.
In England, trick or treating does take place much, particularly in working class neighbourhoods. On the whole, however, it is frowned upon as a form of begging and as a negative part of American global culture.
Halloween is also know by other names:
All Hallows Eve
The Feast of the Dead
The Day of the Dead
Halloween in Welsh is 'Nos Calan Gaeaf'.
Halloween is correctly spelt as Hallowe’en.
Black cats were originally believed to protect witches' powers from negative forces.
A pumpkin is really a squash, and comes from the same family as the cucumber.
About 99% of pumpkins sold are used as Jack O' Lanterns at Halloween.
The biggest pumpkin in the world tipped the scales at a whopping 1,446 pounds. This gigantic gourd was weighed in October 2004 at a pumpkin festival in Port Elgin, Ontario, Canada.
The record for the fastest pumpkin carver in the world is Jerry Ayers of Baltimore, Ohio. He carved a pumpkin in just 37 seconds!
The very first jack o' lantern was made out of hollowed out turnips.
Ringing a bell scares evil spirits away.
If you see a spider on this night, it could be the spirit of a dead loved one who is watching you.
To meet a witch, put your clothes on inside out and walk backwards on Halloween night.
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