Samhain is the Gaelic festival that marks the end of summer and the start of winter. It traditionally begins at nightfall on 31 October and runs through 1 November, because the Celtic day was counted from sunset. Its astronomical point, computed as the sun reaching 225°, falls on 7 November 2026. Whether it also began the Celtic year is debated.
Key takeaways
- Samhain is traditionally kept from nightfall on 31 October to 1 November; the Irish name for Samhain night is Oíche Shamhna.
- Julius Caesar wrote in The Gallic War (6.18) that the Gauls counted time by nights, not days.
- The bronze Coligny calendar, found in 1897 and now at the Lugdunum museum in Lyon, names a month SAMON.
- By our computation, the sun reaches 225°, the astronomical cross-quarter, on 7 November 2026, the same instant as China’s Lidong.
- In a 2017 Current Biology study of 5 adults camping in winter, melatonin onset came about 2.6 hours earlier under natural light alone than under electric lighting.
When is Samhain in 2026?
Samhain runs from nightfall on Saturday 31 October 2026 to Sunday 1 November 2026. It starts the evening before because a Gaelic day began at sunset. It is one of four Gaelic seasonal festivals, with Imbolc (1 February), Beltaine (1 May) and Lughnasadh (1 August).
Some people also mark an astronomical Samhain: the moment the sun reaches 225° of ecliptic longitude, halfway from the autumn equinox (180°) to the winter solstice (270°). The Hong Kong Observatory’s table of the 24 solar terms puts Lidong, Winter Commences, at the same 225°.
| Marker | Date | Set by |
|---|---|---|
| Samhain eve (Oíche Shamhna) | Evening of 31 October 2026 | Tradition |
| US daylight saving time ends | 1 November 2026, 2 AM | US law: first Sunday in November |
| Sun at 225° (Lidong) | 7 November 2026, 9:51 AM UTC | Our computation |
Why did Celtic days begin at nightfall?
According to Julius Caesar, because the Gauls traced their descent from a god of the underworld. Caesar says the druids taught that the Gauls descended from Dis, and that therefore “they determine all periods of time by the number, not of days, but of nights” (H. J. Edwards’s 1917 translation). In birthdays and the beginnings of months and years, he adds, day follows night.
Caesar described Gaul, not Ireland, but Irish festivals follow the same pattern and begin on the evening before.
What is the Coligny calendar, and what does SAMON mean?
The Coligny calendar is an engraved bronze calendar from Roman Gaul. About 150 of its fragments turned up during farm work at Coligny, in the Ain department of France, in 1897. The Lugdunum museum in Lyon, which displays it, dates it to the second half of the 1st century AD; others place it in the 2nd century.
The museum describes a lunisolar calendar: months follow the moon, and extra months are added to keep pace with the solar year. It covers five years, and its twelve months alternate between 29 and 30 days. One, SAMON, is thought to be related to the word Samhain; a note on its 17th day, usually read as TRINOX SAMONI, the three nights of Samon, may mark a festival. Fimi notes that the calendar seems to start its year in summer, and its reconstructions remain inconclusive.
Was Samhain really the Celtic New Year?
Probably not on the evidence we have. Samhain opened winter, the dark half of the year, but there is no evidence that the year began on 1 November in pre-Christian Ireland. The label traces to John Rhys’s Celtic Folklore (1901), which Fimi says rested on very flimsy folklore evidence, and historian Ronald Hutton finds no medieval evidence that 1 November was a major pan-Celtic festival.
The medieval Irish tale Tochmarc Emire lists Samhain first among the four festivals, the time “when the summer goes to its rest” (Thomas Kinsella’s translation). Its farming role is not in doubt: livestock came down from summer pasture, and food that would not keep was shared at feasts. Irish literature, written down from the 9th century, sets great gatherings and openings to the Otherworld at Samhain: the invasion in the Táin Bó Cúailnge begins then, and the Hill of Ward (Tlachtga) in County Meath is thought to have hosted a great Samhain bonfire.
How did Samhain become Halloween?
Halloween grew from Gaelic Samhain customs meeting the Christian feasts of All Saints (1 November) and All Souls (2 November). The Western Church settled All Saints’ Day on 1 November in the 9th century, and its eve, All Hallows’ Eve, became the night for bonfires, guising from house to house, and divination with apples and nuts.
Clodagh Doyle of the National Museum of Ireland told Catholic News Service in 2017 that University College Dublin’s folklore archives record 19th-century lanterns made from turnips and sometimes potatoes. A ghost turnip lantern from Fintown, County Donegal, donated in 1943, survives as a plaster cast at the museum’s Country Life site in County Mayo. Doyle doubted that evidence would be found linking any one emigrant to carrying the custom to America.
How is Samhain marked now?
Samhain is both a heritage festival in Ireland and a religious holiday for several Pagan communities. The Púca Festival, which bills Ireland as the birthplace of Halloween, is scheduled for Trim and Athboy, County Meath, from 29 October to 1 November 2026, with a free Lighting of the Samhain Fire in Athboy on 31 October 2026.
- Wiccans keep Samhain as a Sabbat of the Wheel of the Year, and many consider it the holiest.
- Druids of the Order of Bards, Ovates and Druids describe it as a festival of the dead and of remembrance, around 31 October in the north and 1 May in the south.
- Celtic Reconstructionist Pagans take 31 October as an approximate date, and many adjust it to local climate, such as the first frost.
What do long autumn nights do to the body clock?
The body clock tracks lengthening nights, mainly when people live by natural light. The National Institute of General Medical Sciences says light and dark have the biggest influence on circadian rhythms, through a master clock in the brain that steers evening melatonin.
Two small field studies in Colorado point that way. In 2013, 8 adults camped for a summer week without electric light; their daytime light rose more than fourfold and melatonin onset moved about 2 hours earlier. In 2017, 5 adults camped near the winter solstice: melatonin onset came about 2.6 hours earlier than under electric lighting, and their biological night lasted about 14.4 hours, against 10.0 hours for the 2013 summer campers.
| Tradition says | Science says | Grade |
|---|---|---|
| The day begins at nightfall | Under natural light, biological night begins near sunset (2013) | plausible |
| Samhain opens the dark half | Biological night ran about 4.4 hours longer for winter than summer campers (2017) | plausible |
| Spirits cross over on Samhain night | No health claim | cultural |
More on light’s circadian impact and on when a year begins: New Year or New Season?.
Your day on My BodyClock
The day above on My BodyClock is a late-autumn day built to stay steady as nights lengthen: a fixed 6:30 AM wake time, a walk in morning daylight, another outdoors at midday, errands before dark and dinner at a regular hour. After dinner the lamps go warm and low before a 10:30 PM bedtime. These anchors are our suggestion, drawn from the light research above.
Build yours in Owaves: Owaves: My BodyClock on the App Store, the Android waitlist, or the Body Clock Type quiz. For seasonal planning, see Seasonal Day Plans and World Mental Health Day: Light, Rhythm and Your Mind.
FAQ
When does Samhain start and end?
Samhain traditionally starts at nightfall on 31 October and ends on 1 November, because Gaelic days began at sunset. Many modern Pagans in the Southern Hemisphere mark it around 30 April to 1 May.
Is Samhain the same as Halloween?
No, but they are related. Halloween is the eve of All Saints’ Day, and it took on Samhain customs such as bonfires, guising and carved turnip lanterns. Most American Halloween traditions came with Irish and Scottish immigrants.
Why is Samhain sometimes dated around 7 November?
That is the astronomical cross-quarter, when the sun reaches 225°, halfway from the autumn equinox to the winter solstice. By our computation it falls on 7 November 2026, the same moment as China’s solar term Lidong.
How do you pronounce Samhain?
In English it is usually said SOW-in or SAH-win. The Irish for Samhain night, Oíche Shamhna, sounds roughly like EE-hə HOW-nə.
Sources
- Julius Caesar, trans. H. J. Edwards. The Gallic War, Book 6. Loeb, 1917; LacusCurtius, University of Chicago. https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Caesar/Gallic_War/6B*.html
- Lugdunum — Musée et théâtres romains. “Le calendrier gaulois.” https://lugdunum.grandlyon.com/fr/Oeuvre-incontournable/2381-Calendrier-gaulois-de-Coligny
- Wikipedia. “Samhain.” https://en.wikipedia.org/wiki/Samhain
- Dimitra Fimi. “Samhain or Halloween?” Gramarye 11, 2017; posted 28 October 2019. https://dimitrafimi.org/2019/10/28/samhain-or-halloween-the-ancient-celtic-year-in-contemporary-childrens-fantasy/
- Sarah Mac Donald, Catholic News Service. Catholic Review, 30 October 2017. https://www.archbalt.org/irish-folklife-expert-says-halloween-traditions-began-ireland/
- Púca Festival. “Púca Festival 2026.” https://pucafestival.com/
- Púca Festival. “Lighting of the Samhain Fire.” https://pucafestival.com/event/the-samhain-fire/
- Discover Boyne Valley. “Púca Festival 2026.” https://www.discoverboynevalley.ie/whats-on/puca-festival-2026
- Order of Bards, Ovates and Druids. “Samhain Festival.” https://druidry.org/druid-way/teaching-and-practice/druid-festivals/samhain-festival
- Hong Kong Observatory. “The 24 Solar Terms.” https://www.hko.gov.hk/en/gts/time/24solarterms.htm
- NIST. “Daylight Saving Time.” https://www.nist.gov/pml/time-and-frequency-division/popular-links/daylight-saving-time-dst
- NIGMS. “Circadian Rhythms,” 2025. https://www.nigms.nih.gov/education/fact-sheets/Pages/circadian-rhythms
- Wright KP et al. Current Biology, 2013. https://doi.org/10.1016/j.cub.2013.06.039
- Stothard ER et al. Current Biology, 2017. https://doi.org/10.1016/j.cub.2016.12.041
- NicDhàna et al. The CR FAQ, “Ritual,” 2006. https://www.paganachd.com/faq/ritual.html
- Nancy Ramsey. “Sabbat.” Contemporary American Religion. https://www.encyclopedia.com/religion/legal-and-political-magazines/sabbat
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