# Ancient Eight-part Year

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1. Apr 14, 2017

### Helios

What were the methods of time-keeping for northern Europe before the Christian epoch and apart from the Julian calendar? Apart from lunar reckoning, there is also historical mention of an eight-part solar year, with solstices, equinoxes, and cross-quarters.
Today there are "neo-pagans" who have their models of an eight-part year, but they merely attach their cross-quarter days to the Julian or Gregorian calendar. This is naive because there was no Julian calendar in use there around the very time when this wisdom supposedly originated. The question remains as to how an eight-part year could have been perceived long ago. Unless the reconstruction of an eight-part year method of time reckoning, independent of the counting of days, can be demonstrated, the past existence of an extinct eight-part year remains puzzling.

Let's look at the mathematics of this. Let's suppose an eight-part year is defined by the Sun's ecliptic longitude = 0°, 45°, 90°, 135°, 180°, 225°, 270°, 315°. We'll also find the special latitude L* where the summer Sun rises at north-east and sets at north-west. Here are the relevant equations;

sin ( DECLINATION ) = cos ( LATITIDE ) sin ( AMPLITUDE )
sin ( DECLINATION ) = sin ( ECLIPTIC LONGITUDE ) sin ( OBLIQUITY )
[ SQR 2 ] sin ( OBLIQUITY ) = cos ( L* )
[ SQR 2 ] sin( AMPLITUDE ) = sin( ECLIPTIC LONGITUDE ) at L*

The special latitude L* is approximately 55.7682°. Here, the year can be tracked by the azimuth of sunrise from the east at 0°, 30°, 45°, 30°, 0°, -30°, -45°, -30°, or likewise for sunsets from the west. Because all these angles can be easily drawn by any geometer, unlearned in the ways of trigonometry, I think the peoples long ago, indigenous to this vicinity of this special latitude would have discovered this for themselves and it is here that the eight-part year could have originated and be used as seasonal measure.
I know there are little issues like refraction, the apparent size of the sun's disc, or the slightly unequal duration of the eight parts due to the Earth's eccentric orbit.

2. Apr 15, 2017

### Algr

The ancients were interested in astronomy and calendars because it helped them farm. Equinoxes and solstices provide a natural division of the year into four parts, but nothing particularly important happens half way between one and the other. The correct time to plant seeds would be the same each year, but different in different locations. So you need someone who can say "The solstice was 71 days ago, it's time to start plowing."

The other calendar influencer would be the moon. This produces 13 per year, but drifts slowly, and so isn't as good for farmers. Hunters though would find the moon more important. When they notice something like the full moon rising before the sun has set, they know it is now spring.