The wheel of the year

[kengr]

This is mostly for fayanora, but others may find it useful.

Most societies in temperate climates had eight sun-related festivals. We don't have a name for them as a group anymore. But one of the older names is "the wheel of the year".

These are based on the position of the sun (actually on the earth's position in its orbit).

There are three main ways you can track the sun's position over the course of the year.

First, you can (if you have a clear enough horizon) set up a spot and when the sun rises each morning have an assistant at the end of a long rope place a stick in the ground. Do this every day and you'll get an arc of sticks. You want the long rope so that the sticks are far enough apart.

If you prefer, you can do the same sort of thing at sunset.

The final way is to have a pole stuck in the ground, and every day mark the point at which its shadow is longest.

With the sunrise/sunset methods, you find that each day the sun rises/sets a bit farther over until one day it starts moving back the other way. Six months after that it again reverses direction.

With the noon shadow method the shadow keeps changing length until it hits a minimum or maximum length and then starts changing length in the other direction (ie getting longer instead of shorter or shorter instead of longer. If you are between the Tropic of Cancer and the Tropic of Capricorn, the shadow will actually hit zero length at some points as the sun will be directly over head. And then it switches to the other side of the pole.

If you are exactly on one of the tropics, the line just hits zero length and starts getting longer again. In fact, that's *how* the tropics are defined. They are the latitudes at which the sun is directly overhead at noon on one of the solstices.

The Arctic and Antarctic circles are defined in a similar way. If I recall correctly, they are where the sun never sets on one of the solstices and never rises on the other.

Ok, we'll go with sunrise marking just to make it simpler.

so, standing at your observation point, you have your arc of sticks (or stones or whatever you used to mark the sunrises).

The one at one end of the arc, marks the winter solstice. The one at the other end, marks the summer solstice. And halfway between is where the sun rises on the equinoxes.

So you place a more permanent marker at those three spots.

S-------E-------W

That gives us four festivals. So where are the other 4? Simple. You place a marker in the middle of each of the "gaps".

S---Q---E---Q---W

Those mark the cross-quarter days. Just as with the equinoxes, you hit each of those spots twice during the year. Once while moving left and once while moving right.

The two diagrams above are correct for sunrise in the northern hemisphere or sunset in the southern hemisphere. You flip the ends if you are measuring sunset in the northern hemisphere or sunrise in the southern.

Anyway, this gives you a festival every 45-46 days (about 45.6). And they tend to match well with the seasons in the temperate zones.

So lets list things (using the Celtic names for the cross quarter days) for the northern hemisphere. And listing the Earth's position in its orbit (in degrees).

000 Vernal Equinox (late march)
045 Beltane (early May)
090 summer solstice (late june)
135 Lughnasad (early august)
180 autumnal equinox (late september)
225 Samhain (early November)
270 winter solstice (late december)
315 Imbolc (early February)

http://www.archaeoastronomy.com/ has a nice animated display of this. As well as tables showing the dates & times for various time zones and years.

These points in the year were *important*. There wasn't much point to subdividing things farther as the seasons tend to fluctuate a lot anyway. Plus, why have a 23 (22.8) day cycle when you have the lunar month at ~ 28 with an easy to observe subdivision into 4 parts (full, new and the two quarter moons).

Of course the lunar cycle and the solar cycle don't line up well. The kinda match up over a 19 year cycle, but....

And from all this you see why calendars can be a mess.

Comments

[xander-opal.livejournal.com]

My father used this to his advantage when laying out barns with rows of stalls for calves. The roof was open for fresh air and sunlight, but with a height so that there'd be shadow in the back during summer. After the first was built, he measured the shadow length on the winter Solstice, and used that as the separation for the next barn. This made sure that there was sunlight to keep the calves warm in the winter.