Have you ever wondered why we have Winter, Spring, Summer, Fall, and then Winter again? And why our days almost never have the same amount of daylight? It’s because when God created the Earth, he made it so that the axis it rotates on (every 24 hours) is not at a perfect 90 degree angle to the ecliptic plane of the Earth’s orbit (365 days) around the Sun. This causes the amount of sunlight we receive at different places on Earth, to be different. As we get less and less sunlight each day, it causes our spot on Earth to lose a little more heat each day, causing Winter. As the opposite occurs, it causes Summer. Because the Earth’s equatorial plane is bisected by the Earth’s ecliptic plane, at the Equator, every day has the same amount of sunlight and darkness. So, average daily temperatures stay the same throughout the year. At the North pole, and South pole, for half of the year, the Sun does not come above the horizon, during their respective winters. This makes for a cold climate, and a very cold Winter.
What is the Earth’s equatorial plane, and ecliptic plane?
Imagine if the Earth were cut completely in two at the Equator, and then a large piece of paper were inserted between the two halves. That flat surface would be considered the equatorial plane. If the Sun were cut in two at the center, along the line of the Earth’s orbit around the it, and then a large piece of paper were inserted, that would be considered the Earth’s ecliptic plane. The difference in the two angles is approximately 23.5 degrees. You can see the lines representing the equatorial plane, and ecliptic plane, shown on the picture attached to this article. The angle between these two lines stays the same all year long.
How do we know the angle between the Earth’s equatorial plane, and ecliptic plane, does not change throughout the year?
During an entire year (Earth’s complete orbit around the Sun), the North Star will always be in the same place in the sky, when observing it from the same place. Anywhere along the Equator, which is zero degrees latitude, the North Star will always appear to sit right on the horizon. At the Tropic of Cancer, it will appear to be 23.5 degrees above the horizon. At the North Pole, it will be directly overhead. Whatever latitude you are on in the Northern Hemisphere is how far above the horizon you’ll see the North Star. And this is true all year long. If the axis our Earth rotates on wobbled throughout the year, this would not be true. And if Earth moved up and down on its axis throughout the year, as if it were bouncing as it moved along its ecliptic plane around the Sun, then the Sun would not be directly overhead on Summer Solstice along the Tropic of Cancer latitude (23.5 degrees), consistently, every year. Also, the amount of daylight at the Equator would differ every day. Which, it does not.
So what is Spring Equinox, and Fall Equinox?
Imagine looking down at the Earth and Sun, as if you could see the imaginary line drawn by the Earth as it moves around the Sun counterclockwise. Well, if Summer Solstice were 12 o’clock, and Winter Solstice was 6 o’clock, then the Spring Equinox would be at 3 o’clock. Fall Equinox would be at 9 o’clock. At a specific moment in time, if you were looking at the Earth lined up with the Sun, the Earth’s axis would evenly divide the Sun, and so would the Equator. That exact moment is known as an equinox. That day, every place on Earth gets 12 hours of sunlight, and 12 hours of darkness. If you are right at the poles, you only have one day when the sun sets and rises. That is when an equinox occurs. Before, and after that, it’s either the Sun being visible all day, or the opposite. Hence, the name, Land of the Midnight Sun.
Now, for all you obsessive compulsive folks!
There are slight deviations in all of this. The Earth is not perfectly smooth. The Earth’s orbit around the Sun is elliptical. Our atmosphere bends light rays. Etcetera! What I’m trying to do is help folks be able to visualize how the Earth, Sun, North Star, and also the Moon, move relative to one another. And how they all impact one another. I was 40+ years old before I really thought about this a lot. The heavy thinking mostly set in one day when I was trying to figure out how to take photos of the Sun during a solar eclipse. But, that’s another story for another day! Come back and see me again. I plan to write about that, and a few other things I learned as a result of that. Like, how to figure out where you are (approximately) on a sunlit day, with just a stick, a few small rocks, and some time on your hands. See y’all then!