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Earth Notes: Winter Solstice

A pale yellow sun rises over a hazy canyonland, with a conifer tree in the foreground and a sky filled with pink and blue clouds.
Bob Wick
Bureau of Land Management
Winter sunrise at Grand Canyon-Parashant National Monument

The winter solstice is the longest night of the year for those in the Northern Hemisphere. It’s a time traditionally associated with rebirth and renewal, as the sun pauses in its yearly trek.

The solstice is an astronomical event. It happens because the Earth is tilted on its axis, so the sun appears to move along the horizon as it rises and sets throughout the year. Today, it’s at the point farthest south in its path, and appears to pause there before reversing direction and traveling northward again. That’s why the Latin root of the word “solstice” means “sun stands still.”

For millennia people around the world have marked this moment in the sun’s calendar, with celebrations or even grand architectural feats, like Stonehenge in England and Machu Picchu in Peru. On the Colorado Plateau, the Great Houses of Chaco Canyon built by the Ancestral Puebloans are aligned to the cardinal directions and make use of shadows and sunlight.

A famous example is a spiral petroglyph at Fajada Butte known as the Sun Dagger. Sandstone slabs surrounding the petroglyph cause the sunlight on winter solstice to fall in the shape of two daggers, framing each side of the spiral. On the summer solstice, a single danger spears the center.

Today, Hopi and Zuni, who are the descendants of the Ancestral Puebloans, mark the winter solstice with ceremony, as do many peoples around the world. From this point forward, the days will grow longer and the nights shorter as the planet begins to tilt back into spring.

This Earth Note was written by Melissa Sevigny and produced by KNAU and the Sustainable Communities Program at Northern Arizona University.

Melissa joined KNAU's team in 2015 to report on science, health, and the environment. Her work has appeared nationally on NPR and been featured on Science Friday. She grew up in Tucson, Arizona, where she fell in love with the ecology and geology of the Sonoran desert.
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