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Archeoastronomy of the Longest Night

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As our northern hemisphere days begin to lengthen, I like to think about the many ways people have marked the Winter Solstice throughout human history. Like Summer Solstice (the longest day), the equinoxes, and motions of the planets and Moon through the sky, Winter Solstice has long been observed, recorded, and used to construct special buildings.

Some of these buildings were erected so long ago that no written record of their use is available today, but they clearly point at cultures that valued the knowledge of precisely when the longest night of the year occurs. Two ancient cultures in the northern hemisphere whose monuments I’ve visited come to mind: Celtic and Anasazi.

Maeshowe was built ~5000 years ago, making it one of the oldest Neolithic monuments we know of in the world, on Orkney Island in the far north of what is today Scotland. It is a large mound that is green and grassy in the summer, and has a special relationship with the setting Winter Solstice Sun. On December 21, at the end of a dim day when the Sun skims along the horizon, sunlight creeps along a long passageway in the mound and illuminates the back wall of a small stone chamber at the heart of the mound. Long ago people decided that this was an important enough day to warrant building a huge monument to mark its happening.

Maeshowe

The rays of the Winter Solstice setting sun reach the same stone chamber at the center of the Maeshowe mound. Photo by Evie McRae with Creative Commons license.

 

Were they motivated by a spiritual desire to connect to the natural rhythms around them? Were they a small elite group of early astronomers, or were they made up of an entire community of interested individuals? The Maeshowe chamber is too small for more than a dozen or so people to be in at once, so whatever activity happened 5000 years ago in that seemingly sacred space was seen by only a few people at a time. (Note: sunlight actually reaches into the chamber for several days before and after the Winter Solstice, since the sunset moves slowly across the horizon at this time of year…creeping as far north as it will set all year, and then creeping back south along the horizon as the days lengthen again).

 

newgrange

Sunrise at Winter Solstice shines light along a narrow path into the heart of Newgrange. Megalithic art decorates the entrance. Photo by Hofi0006 with a Creative Commons license.

 

Newgrange is located in Ireland, and is also an ancient mound of the same era with a small, central stone chamber and a narrow passageway pointing out to the Winter Solstice sun. In this case, the passage is aligned with sunrise, when sunlight comes in a small stone box above the entryway to shine on the far back wall of the central chamber. Another contrast to Maeshowe is that human (cremation) remains have been found in Newgrange, indicating that it was perhaps a tomb or a site for ritually remembering the dead. Perhaps remembering the dead was linked to the Winter Solstice because the Sun was associated with life and therefore the darkness with death? Or maybe it was a burial tomb for one fantastically powerful ruler, and that person had a special connection to the longest night of the year?

One detail that points to Newgrange and Maeshowe being more than just practical, observational devices for tracking the motion of the Sun in the sky is that the weather is often overcast. Would the Sun shine along these passages every year, or would clouds prevent it nine times out of ten? Was the window of a few days on either side of the Winter Solstice when the Sun rises and sets in approximately the same place on the horizon useful so that at least one of those days every year might be cloud-free? With no written records, it might not ever be clear what the people who built these architectural wonders intended them to be used for.

Another ancient culture that built great structures to mark the motion of the Sun on the horizon is the Anasazi. They also left no written records, but some inkling of their Sun-observation practices and motivations might be gleaned from modern Zuni and Hopi Sun-watchers, who are using the same landscape for their practice, if not necessarily for the same reasons as the people did 900 years ago in what is now southwest Colorado and northern New Mexico.

In Mesa Verde, the two towers of the Sun Temple can be viewed from a special location across the canyon at Cliff Palace such that the Winter Solstice sun rises between them. That special spot is marked with a divot in the rock, and is not far from a tall tower that may have been used to watch the Moon as well, as inferred from pictograms inside the tower that seem to mark out its motion across the horizon, a pattern that repeats every 18.6 years, something a few ancient cultures observed and recorded. This set of buildings had more kivas, circular ceremonial rooms of stone sunken into the ground, per house than any other village in Mesa Verde, itself a hub of agricultural and ritual life ~900 years ago. Apparently keeping close track of the Sun and Moon was important at Cliff Palace, and perhaps for the entire community who lived in the area.

One mystery about the site remains unsolved though: were the towers the Sun rises between tall enough to see from Cliff Palace, or was the apparently unfinished structure of the Sun Temple, and indeed the entire set of villages in Mesa Verde, abandoned before it could be regularly used? Was there a temporary wooden structure built on the Sun Temple tower foundations every year, or was the divot at Cliff Palace used only to determine where to build the Sun Temple in the first place?

Sun Temple

From across the canyon, the Winter Solstice Sun appears between the two circles in this Sun Temple. National Park Service photo.

 

Further south and east is the collection of Chaco Canyon villages that were built at the same time, when perhaps the climate was more conducive to farming and supporting large populations in what is now an arid landscape. Again a special location in one village, in this case a room with an unusual corner-window in the Pueblo Bonita archeological site, has a great view of the horizon, and is oriented such that the Winter Solstice sunlight would come through the window and illuminate the back wall of the room.

Nearby is perhaps the most convincing Anasazi archeological site for telling us, without words, that they carefully watched the Sun throughout the year. A huge butte sticks up out of the landscape, with several giant slabs of stone leaning against its side. Behind one of these are a few petroglyphs, spirals carved into the stone. They precisely mark the solstices and equinoxes. The Winter Solstice Sun, around midday, creeps through gaps between two slabs of stone and sends two narrow daggers of light down the rock behind them, along either side of the larger of the spirals. At Summer Solstice, instead one light dagger pierces the middle of the spiral, and at equinoxes a smaller nearby spiral is traced down its center by a smaller dagger of light. (See an animation.) Clearly this location was a place to confirm the special days of the Sun’s motion in our sky. Today Sun-watchers in local cultures keep track of the Sun’s motion both for the sake of timing important ceremonies and to let their communities know when it is time to plant seeds, two aspects of life that perhaps cannot be disentangled. Was this true for people at Chaco Canyon and Mesa Verde? Were their Sun-watching practices pragmatic, ceremonial, or both?

All we really know in the case of Neolithic structures built in Ireland and Scotland ~5000 years ago, and in the case of markers of the Sun’s motion used by people in the southwestern United States ~900 years ago, is that they built precisely aligned structures to mark the special days they observed year after year, particularly when the Sun was the lowest in the sky and up for the shortest amount of time. Just like today, the coming of longer days was likely a cause for celebration by the communities that created these amazing examples of archeology.

Happy lengthening of the days!

Michelle Selvans is a geophysicist in the Center for Earth and Planetary Studies at the National Air and Space Museum.

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2 thoughts on “Archeoastronomy of the Longest Night

  1. Happy lengthening of the days! too you to…..
    Very interesting…..
    liked the pictures…

    FUN TO READ….!!!!!!

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