Illustration by NASA
Halloween, Oct. 31, falls between the September equinox and the December solstice and so is a cross quarter day, equinox being when the sun sets due west and solstice when the sun sets at its most northern or southern point on the horizon.
There are four of these cross quarter days, each celebrated as a holiday. They are Groundhog Day February 2, May Day May 1, Lammas Aug. 1 and Halloween Oct. 31 (which astronomical calendars say the cross quarter actually is November 7.
According to one of the Celtic calendars, Groundhog Day is also Candlemas and the beginning of Spring. But one of the Celtic calendars divides the year into three parts with Midsummer Day and Christmas being the other two parts instead of the four quarter days.
Also, check out this lecture from Ohio State University: Telling Time. It is very informative. If you scroll down a bit you find the cross quarter days and there dates and names according to different calendars and groups.
For more info go to EarthSky, Space and Telescope and Farmer’s Almanac.
