The Flying Figure Eight

Sun Spots  An analemma is the shape you’d get if you photographed the sun from the same spot at the same time every day for a year and traced the pattern. The sun’s yearly journey through the sky makes a slightly stretched figure eight pattern. –timeanddate.com 

You read it first in this week’s The Factory in Guide magazine.

Ana-what? A·nuh·leh·muh, the phonetic spelling of analemma, is the figure eight shape our sun creates yearly in its journey across the sky. This shape can be plotted on a graph, showing the whereabouts of the sun if viewed from the same place at the same time on any given day of the year. 

Each analemma is unique. There are many variables to the creation of an analemma. First, let’s talk about the two main factors that give analemmas that basic figure eight shape and what would happen if they were different. These two factors are Earth’s elliptical orbit around the sun and the tilt of the planet’s axis. 

Did you know that Earth doesn’t orbit the sun in a perfect circle? Or that the sun isn’t even at the center of our orbital path?! Our planet orbits the sun in a stretched, circular shape called an ellipse. This means that Earth is closer to the sun at some points and farther away for others. With a basic understanding of gravity, we can know that when Earth is closest to the sun, its pull on our planet will strengthen, causing our orbital speed to increase. When Earth is farthest from the sun, its pull is weaker, and our orbital speed will slow. If the tilt of Earth remained the same, but its orbital path became a perfect circle with the sun at its center, the generation of analemmas would have perfectly shaped figure eights in the sense that both loops would be the same size. The Earth’s elliptical orbit is what gives our analemmas their two distinctly sized loops.

Our planet has a tilt of 23.5 degrees from its orbital plane. Because of this fact, the sun appears as if it is moving up and down throughout the year. This is what causes analemmas to have two loops. During the summer, the sun reaches its highest position in the sky resulting in the longest day of the year, summer solstice, on June 21st. On December 22nd, the shortest day of the year known as winter solstice, the sun will appear its lowest in the sky. These two dates are important to the generation of analemmas because they are the farthest end points of the two loops. If the orbital path of the Earth remained the same but its axis not tilted, the resulting analemmas would appear oval shaped. 

So now we know how the tilt of the Earth and its elliptical orbit are what give analemmas their basic shape, but what are the other variables that can manipulate it? Well, which hemisphere you reside in can have an effect on it. Those of us in the northern hemisphere will have analemmas with the smaller loop on top and those in the southern hemisphere will have the smaller loop on the bottom. 

Your exact location can also manipulate the shape in terms of its angle. The closer to the poles you get, the more the analemma will appear to be straight upright, and the closer to the equator, the more the analemma will appear to be horizontal, like the infinity symbol. The time of day will also change the shape in terms of its direction. 

With all of these variables, it’s no wonder that analemmas have completely different shapes for the varying planets in our solar system. Uranus and Neptune share the figure eight shape with Earth—as does Pluto, whether it’s a planet or not.

As we consider the shapes of analemmas and the amazing God who has put the planets and stars in their place, it’s hard to know whether they are a masterpiece of art or science!