In a universe where everything tends to coagulate into a sphere, the circle seems the logical choice. It is also the basis of the symbol of the circle with a dot in the center, the symbol we commonly use for God. Plato once said, “God always geometrizes.” The Circle of Illumination, along with the tilt of the Earth on its axis, forms the geometry of the seasons. The North and South Poles would only see the Sun barely peeking above the horizon all day long. The Sun’s rays would be perpendicular to the Earth’s equator 365 days a year, and there would be no seasons.
If the Earth weren’t tilted at all, the Circle of Illumination would remain constant. If the tilt were greater, the Arctic Circle would be drawn farther south on the globe, because that’s where the Circle of Illumination would reach. Since the Earth is tilted on its axis by 23.5 degrees, the Arctic Circle is 23.5 degrees south of the North Pole. This happens on June 22nd every year, the day the Sun enters the Zodiacal sign of Cancer-hence the name “Tropic of Cancer.” The word “tropic” means “turning towards.” At noon on that day, a flag pole casts no shadow.
The Tropic of Cancer is the farthest northern point where the Sun’s rays can be perpendicular to the Earth, when the Sun appears directly overhead. This is the point where the Sun never goes below the horizon in the Summer, which is why they call the Arctic the “land of the midnight Sun.” The Arctic Circle, for example, is the farthest point south that the Sun’s rays can reach when the Earth’s North Pole is tilted toward the Sun. Ever wonder what those lines on a globe mean, the ones that say Arctic Circle, Tropic of Cancer (and Capricorn), and the Equator? Well, they have to do with what’s called the “Circle of Illumination,” which is the half of the Earth that’s illuminated by the Sun.
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