ancient calendar

At its heart, Halloween is an astronomy holiday. It’s a day rooted in Earth’s orbit around the sun. It’s a cross-quarter day and a testament to our ancestors’ deep understanding of the sky. 

October 31 marks the approximate midway point between the September equinox and the December solstice. This means Halloween also an astronomy holiday, and one of the year’s four cross-quarter days. 

Learn about the four seasonal Quarter Days in the ancient Celtic calendar.

Some historians are divided as to whether the ancient Celts observed the solstices and equinoxes (quarter days). Some believe that the Celts divided the year into just four major sections: Samhain, Imbolc, Beltane, and Lughnasadh (cross-quarter days). 

Together, the Quarter Days and Cross-Quarter Days made an eight-part year that reflected the natural progression of the seasons. Maybe the ancient Celts observed all eight divisions of the year- although no evidence remains to support this. 

The days that marked the four major divisions of the year were called quarter days. They marked the solstice - when the sun sets at its most northern or southern point on the horizon; and equinox - when the sun sets due west. Marking the natural rhythm in the way people farmed.

Halloween, an astronomy holiday

As the Roman calendar was adopted - twelve months that marked both civil and religious purposes - all of the Celtic days began to conform as well. More closely aligning with the liturgical year of the Christian church that became identified with major religious festivals. 

The four cross quarter days marked the midpoint between each solstice and equinox. For the ancient Celts, these signaled the beginning - not the middle of a season. With the major two divisions being winter (Samhain) - starting the dark half of the year; and summer (Beltane) - starting the light half of the year.