I have a few questions which are probably the most stupidest and obvious questions of ever, but bear with me please!
Every time a sabbat rolls around I get confused on the date. It's because I know the Celts viewed the day as beginning at sundown (so, for example, Friday will begin at sundown tonight), and I'm wondering if that's how the calendars list them? Let me put it this way. Say the Calendar says Jun 21st is the Summer Solstice. Does that mean it begins on Jun 21st and then goes through the 22nd? Or is it just Jun 21st by itself?
The other question is, is Imbolc celebrated on Feb 1 or 2? I've seen them both listed so many times, but I'm wondering specifically when the Celts celebrated as I'm wanting to keep my path as Celtic as possible, though I'm not a Celtic Reconstructionist :P
These are not stupid questions, and they are most certainly not obvious, as there is no certain answer to them.
The ancient Celts did not use the Gregorian calendar. In fact, the ancient Celts did not all use the same calendar. One calendar we do have in the archaeological record is the Coligny calendar:
It is a lunisolar calendar. Partially inspired by that information, I created my own lunisolar calendar for modern paganism:
OK, more specifically:
Solstice: The Celts didn't celebrate the solstice, in anything I've seen. So you need to decide what calendaring rules you wish to use. You said that you define your day as sunset to sunset. So you look up the exact time of the solstice or equinox for that year. This year, Sol entered Capricorn at 0530 GMT on Thur. 22 Dec. That's 2330 CT on Wed. 21 Dec. for me. Using those rules and my location, the Winter Solstice started at sunset on Wed. 21 Dec and ends at sunset on Thur. 22 Dec.
Imbolc: Again, the ancient Celts didn't use the Gregorian calendar, so what we are working with are two Christian feasts that were later associated with the mentions of the ancient feast of Imbolc. Part of the confusion is that there are two critical and related feasts at the beginning of February in Irish Catholicism: The Feast of St. Brigid on 1 Feb; and Candlemas, or the Feast of the Purification of the Virgin, on 2 Feb. These feasts are interrelated in the Irish consciousness in that 1 Feb honors St. Brigid, Mary of the Gael, while 2 Feb. honors St. Mary, Mother of God. (In some legends, Brigid is even declared to have been Mary's midwife at the birth of Jesus.) Given that the other three cross-quarter days are all observed on the first day of the month--beginning on the eve before--I would suggest starting Imbolc at sunset on 31 Jan. and ending at sunset on 1 Feb.