I remember the Celtic agricultural festival days every year on In Season. I like agricultural calendars because they focus on Earth-based rhythms, which works for a gardener like me. We humans use a mish-mash of ways to mark the cycle of seasons and the passage of days. We use solar, lunar, astronomical, meteorological and climatological reference points. Probably every indigenous society across the Earth has hunter-gatherer-gardener based festivals.
The other days listed, the solstices and the equinoxes are astronomical days which use astronomy, namely the sun, as the reference for. The astronomical seasons are based on the place of the Earth to the Sun.
The meteorological and climatological seasons are different from the astronomical seasons. The meteorological and climatological seasons are based on weather and local annual climate. These seasons divide the year into quarters which each season consisting of three months each. Spring is counted as March, April and May with May 1st marking the beginning of spring. Meteorological summer includes June, July, and August with June 1st marking the beginning of summer. Meteorological fall includes September, October, and November with September 1st marking the beginning of Autumn. Meteorological winter includes December, January, and February with December 1st marking the beginning of winter. More information on the differences are here.
Imbolc (February 1st or 2nd) – The Beginning of Spring on the Celtic Agricultural Calendar
Imbolc is a Celtic festival marking the beginning of spring. Most commonly it is celebrated on 1 or 2 February (or 12 February, according to the Old Calendar) in the northern hemisphere and 1 August in the southern hemisphere. These dates fall about halfway between the Winter Solstice and the Spring Equinox.
Imbolc is usually celebrated when the first stirrings of spring are felt, or on the full moon that falls closest to this time.
The holiday was, and for many still is, a festival of the hearth and home, and a celebration of the lengthening days and the early signs of spring. Celebrations often involved hearth fires, special foods (butter, milk, and bannocks, for example), divination or watching for omens, candles or a bonfire if the weather permits. Imbolc is traditionally a time of weather prognostication and the old tradition of watching to see if serpents or badgers came from their winter dens. This is a precursor to the North American Groundhog Day.
Date: February 1 or 2 in the northern hemisphere; August 1st the southern hemisphere
Related to: Candlemas, Groundhog Day
Observed by: Gaels (Irish, Scottish and Manx people), Neopagans (Celtic Reconstructionists, Neo-Druids and Wiccans)
Spring Equinox (March 20th or 21st in the northern hemisphere)
Day and night are equal length at about twelve hours each. The Earth does not point toward or away from the sun. On this date the sun rises exactly in the east and sets exactly in the west.
Beltane (May 1st) -The Beginning of Summer on the Celtic Agricultural Calendar
Beltane is a cross-quarter day, marking the midpoint in the Sun’s progress between the spring equinox and summer solstice. It is the traditional first day of summer in Ireland, Scotland and Isle of Man. Beltane marked the beginning of summer and was linked to similar festivals held elsewhere in Europe. The date for this midpoint varies from year to year between May 5th or May 7th. The practice of decking the May Bush/Dos Bhealtaine with flowers, ribbons, garlands and colored egg shells is found among the Gaelic diaspora, most notably in Newfoundland, and in some Easter traditions on the East Coast of the United States. Celebrations included lighting bonfires, making ‘May boughs’ or ‘May bushes’, dancing, singing, feasting.
Also called: Irish: (Lá) Bealtaine, Scottish Gaelic: (Là) Bealltainn, in Manx : (Laa) Boaltinn/Boaldyn
Date: May 1 in the northern hemisphere; October 31 in the southern hemisphere
Related to: May Day, Calan Mai, Walpurgis Night
Observed by: Gaels, Irish people, Scottish people, Manx people, Neopagans
More about Beltane – http://en.wikipedia.org/wiki/Beltane
Summer Solstice (June 20th – 22st in the northern hemisphere)
The summer solstice is the longest day of the year and has the shortest night.
Lughnasadh (July 31st or August 1st) – The Beginning of the Harvest on the Celtic Agricultural Calendar
Lughnasadh is a cross-quarter harvest festival halfway between the Summer Solstice and the Autumnal Equinox. Lughnasadh is a traditional Gaelic holiday celebrated on August 1st in the northern hemisphere and February 1st in the southern hemisphere. Celtic Reconstructionists who follow Gaelic traditions tend to celebrate Lughnasadh at the time of first fruits, or on the full moon that falls closest to this time. In the Northeastern United States, this is often the time of the blueberry harvest, while in the Pacific Northwest the blackberries are often the festival fruit.
In Gaelic Ireland, Lughnasadh was a favored time for handfastings — trial marriages that would generally last a year and a day, with the option of ending the contract before the new year, or later formalizing it as a more permanent marriage.Festival celebrations included Offering of First Fruits, Bonfires, Feasting, and Handfasting.
Also called: Lúnasa (Modern Irish), Lùnastal (Scottish Gaelic), Luanistyn (Manx Gaelic); Lammas (England); Calan Awst (Wales)
Date: July 31 in the northern hemisphere; January 31 in the southern hemisphere
Observed by: Historically: Gaels Today: Irish people, Scottish people, Celtic neo-pagans
More on Lughnasadh – http://en.wikipedia.org/wiki/Lughnasadh
Autumn Equinox (September 20th -22nd in the northern hemisphere)
Day and night are equal length of twelve hours each. The Earth does not point toward or away from the sun. On this date the sun rises exactly in the east and sets exactly in the west. The season is called, “Fall” in areas where leaves “fall” from the trees.
Samhain (October 31) – The End of the Harvest on the Celtic Agricultural Calendar
The medieval Gaelic festival of Samhain marked the end of the harvest, the end of the “lighter half” of the year and beginning of the “darker half”. It was celebrated over the course of several days and had some elements of a Festival of the Dead. Bonfires played a large part in the festivities. People and their livestock would often walk between two bonfires as a cleansing ritual, and the bones of slaughtered livestock were cast into its flames. The festival includes celebrations include bonfires, guising, divination, apple bobbing, and feasting.
The date of Samhain was associated with the Roman Catholic All Saints’ Day (and later All Souls’ Day) from at least the 8th century, and both the secular Gaelic and the Catholic liturgical festival have influenced the secular customs now connected with Halloween.
Dates: October 31st in the northern hemisphere; April 30th in southern hemisphere
Observed by: Historically: Gaels; Today: some Irish people, Scottish people, and Celtic neopagans
Also called: Samhain (Scottish Gaelic), Sauin (Manx Gaelic), Oíche Shamhna (Irish)
More on Samhain – http://en.wikipedia.org/wiki/Samhain
Winter Solstice (December 20th – 22nd in northern hemisphere)
The shortest night and longest day of the year.
Seasons Calculator http://www.timeanddate.com/calendar/seasons.html
Equinoxes, Solstices and Cross-Quarter Days http://www.archaeoastronomy.com/seasons.html