Okay Tony-san - I hear you on the lunar calendar thing - the only problem is that we've had so many calendars throughout human reckoned time - who's to say? By solar reckoning - which our current calendar is only off by 1/4 of a day each of our "years" - it's pretty close - hence the solstices and equinoxes are determined that way - and Halloween - or Samhain - is halfway between the summer solstice and the autumnal equinox if I remember correctly referred to as "cross-quarter day" - from a time when observing nature around us was more important than our computers or televisions!
So by some accounts - the day is figured on a solar calendar - some probably by the lunar one... - like Easter and Christmas - the official date depends on who's in charge I guess.
Anyway - here's some history on Halloween...
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McBain's Etymological Dictionary of the Gaelic Language says that "samhuinn" (the Scots Gaelic spelling) means "Hallow-tide" (the holiday), probably from roots meaning "summer's end;" with a possible derivation from the annual assembly at Tara every November 1st. MacFarlane's School Gaelic Dictionary defines it simply as "Hallowtide." ... "samhain" or "La Samhna" (to use the Irish spellings) is the first of November, or the month of November, or "Hallowtide/Halloween."
There were four Major High Days celebrated by the Paleopagan Druids throughout the Celtic territories: Samhain, Oimelc, Beltane & Lughnasadh (in the Irish spellings). Four additional High Days (Winter Solstice or "Midwinter," Spring Equinox, Summer Solstice or "Midsummer," and Fall Equinox), which are based on Germanic or other Indo-European cultures, are also celebrated in the Neopagan Druid calendar, along with others based on mainstream holidays (visit the linked essay for details).
The most common practice for the calculation of Samhain, Oimelc, Beltane & Lughnasadh has been, for the last several centuries, to use the civil calendar days or eves of November 1st, February 1st, May 1st and August 1st, respectively. [snip]The Celtic Fire Festivals
These four major holy days are traditionally referred to as "fire festivals" because to the ancient Celts, as with all the Indo-European Paleopagans, fire was a physical symbol of divinity, holiness, truth, and beauty. Whether in Ireland or India, among the Germans or the Hittites, sacred fires were kindled on every important religious occasion. To this very day, among Eastern and Western Catholics, you can't have a satisfying ritual without a few candles being lit -- of course, the Satanic Panic-ers consider them Heathen too!
Samhain or "Samhuinn" is pronounced "sow-" (as in female pig) "-en" -- not "Sam Hain" -- because "mh" in the middle of an Irish word is a "w" sound. It's known in Modern Irish as Lá Samhna, in Welsh as Nos Galen-gaeof (that is, the Night of the Winter Calends), and in Manx as Laa Houney (Hollantide Day), Sauin or Souney. Samhain is the most important of the fire festivals, because it marks the Celtic New Year (a week later the Celt's Indo-European cousins in India celebrate Divali, which is their New Year's festival). Samhain was the original festival that became "All Saints' Day" in the Christian calendar. Since the Celts, like many cultures, started every day at sunset of the night before, this became the "evening" of "All Hallows" ("hallowed" = "holy" = "saint") which was eventually contracted into "Hallow-e'en" or the modern "Halloween."
Among other things, Samhain is the beginning of the Winter Half of the Year (the seasons of Geimredh & Earrach) and is known as "the Day Between Years" (the year, like the day, began with its dark half). The day before Samhain is the last day of the old year and the day after Samhain is the first day of the new year. Being "between years," it is considered a very magical time, when the dead walk among the living and the veils between past, present and future may be lifted in prophecy and divination.
Many important mythological events are said to have occured on that day. It was on a Samhain that the Nemedians captured the terrible Tower of Glass built by the evil Formorians; that the Tuatha De Danann later defeated the Formors once and for all; that Pwyll won his wife Rhiannon from Gwawl; and that many other events of a dramatic or prophetic nature in Celtic myth happened. Many of these events had to do with the temporary victory of the forces of darkness over those of light, signaling the beginning of the cold and dark half of the year.
There is some evidence to indicate that three days were spent celebrating this festival. Philip Carr-Gomm, Chosen Chief of the Order of Bards, Ovates and Druids, speaking of both Paleopagan and Mesopagan Druids in England, had this to say about it in his Elements of the Druid Tradition:
Samhuinn, from 31 October to 2 November was a time of no-time. Celtic society, like all early societies, was highly structured and organised, everyone knew their place. But to allow that order to be psychologically comfortable, the Celts knew that there had to be a time when order and structure were abolished, when chaos could reign. And Samhuinn, was such a time. Time was abolished for the three days of this festival and people did crazy things, men dressed as women and women as men. Farmers' gates were unhinged and left in ditches, peoples' horses were moved to different fields, and children would knock on neighbours' doors for food and treats in a way that we still find today, in a watered-down way, in the custom of trick-or-treating on Hallowe'en.
But behind this apparent lunacy, lay a deeper meaning. The Druids knew that these three days had a special quality about them. The veil between this world and the World of the Ancestors was drawn aside on these nights, and for those who were prepared, journeys could be made in safety to the 'other side'. The Druid rites, therefore, were concerned with making contact with the spirits of the departed, who were seen as sources of guidance and inspiration rather than as sources of dread. The dark moon, the time when no moon can be seen in the sky, was the phase of the moon which ruled this time, because it represents a time in which our mortal sight needs to be obscured in order for us to see into the other worlds.
The dead are honoured and feasted, not as the dead, but as the living spirits of loved ones and of guardians who hold the root-wisdom of the tribe. With the coming of Christianity, this festival was turned into Hallowe'en (31 October), All Hallows [All Saints Day] (1 November), and [All Souls Day] (2 November). Here we can see most clearly the way in which Christianity built on the Pagan foundations it found rooted in these isles. Not only does the purpose of the festival match with the earlier one, but even the unusual length of the festival is the same.
The Christian Church was unable to get the people to stop celebrating this holiday, so they simply sprinkled a little holy water on it and gave it new names, as they did with other Paleopagan holidays and customs. So when Satanic Panic-ers come to your local school board and try to get Halloween removed from the public schools because "it's a Pagan holiday," they are perfectly correct. Of course, Valentine's Day/Lupercalia, Easter/Eostre, and Christmas/Yule also have many Paleopagan elements associated with their dating and/or symbols, as the Jehovah's Witnesses and others have pointed out for decades. So if we decide to rid the public schools of all holidays that have Pagan aspects to them, there won't be many left for the kids to enjoy.<HR></BLOCKQUOTE>
from a page entitled "The Real Origins of Halloween" http://www.witchvox.com/holidays/samhain/1031_realorigins.html