Celebrating solstice: Longest day of the year is Saturday

The longest day of the year soon approaches, and something about that just makes people around the world want to celebrate. Between its reliable astronomical pattern and its life-giving, mega dose of sunlight hours, the summer solstice has inspired many sculptural and architectural sites that mark and celebrate it.

To truly appreciate the marvel of these sites, it’s important to understand the science behind why they work.

“On the summer solstice, the northern hemisphere of Earth is tipped most directly toward our sun, and on this day we receive the most direct sunlight,” Spokane Falls Community College astronomy instructor Michele Moore said.

Earth is tipped at an angle of 23.5 degrees, and that means as it rotates around the sun, things are always a little uneven on either end. Every year that passes, that tilt is always pointing the same direction on that one, long day. (With leap years as regular adjustments since one trip around the sun is actually about 365.2422 days.)

On this day, the sun is also at its highest point in the sky, referred to as solar noon. The height of the sun is measured by the solar elevation angle. If the sun is at the horizon, that’s 0 degrees. If the sun is directly ahead, that would be 90 degrees.

You can actually get a rough estimate of the altitude of any object in the sky without tools. Stick your fist out at arm’s length toward the horizon. One fist stacked on top of the horizon is roughly 10 degrees. Keep stacking your fists until you reach the sun and add them all together.

It’s simple observational methods like these that allowed the prehistoric people to erect structures that would accurately align with the sun’s annual patterns.

Eventually, solar observation got more complex through the observation and measurement of vertical objects and their shadows, called the gnomon method. The most recognizable tool of this method is the sundial. (Fun trivia fact – the part of the sundial that casts a shadow is called a gnomon.)

Imagine you’re an ancient enjoying the longest day of the year with your ancient buds. You’re looking at some vertical object and notice that the shadows of this object are super short today. The sun starts to set and the shadows get longer. This simple observation would open the gateway for humans to more specifically measure time and develop calendars. With the later development of trigonometry, an equation is developed using the length of a gnomon and the length of its shadow to calculate the solar elevation angle.

All of that to say, humans have been great observers of the sun for a long time and understanding that makes it a bit easier to wrap your head around the fact that humans actually didn’t need assistance from aliens to figure this stuff out. Although that cuts back a bit on the mystery factor, it makes the human stories behind the structures even cooler.

One of the oldest known sites to mark the summer solstice is the 7,000-year-old stone circle of Nabta Playa in southern Egypt. Although this site is a desert now, back then it would have featured seasonal lakes to support nomadic peoples. Some argue that within the circle, two sightlines line up with the position of the sun on the summer solstice, which would have helped these nomadic groups predict the arrival of monsoon season.

Another site that is almost just as old is the Goseck Circle located near the center of Germany. It was excavated in the early 2000s and has since been reconstructed. The site is surrounded by a circular moat, and within it are what you could describe as two more fence-like circular structures. These circles have specific gaps in them that align with the sunrise and sunset during winter and summer solstice, allowing Neolithic peoples (the first farmers) to observe and track the sun.

Stonehenge is by far the most popular structure and is slightly more recent with parts of the structure dated to be just more than 5,000 years old. That said, post holes have been discovered near the site that have been dated around 10,000 to 8,000 years old, indicating that prehistoric peoples may have erected poles in this area prior to the construction of the Stonehenge monument. The central axis created by the circular formation points toward where the sun rises on summer solstice. This means if you stand in the middle of Stonehenge and you look toward an outer stone, called the Heel Stone, it will align with the sunrise on Saturday.

This summer solstice while you remark on how wonderful the long sunlight hours are, you can remember there is a long line of humans before you who felt exactly the same way.