Midnight Sun: Earth’s Seasons and How They Change
The lyric “A never-endin’ midnight suuuuuUuuuUuUuUuUun,” popularized by Zara Larsson in her new song Midnight Sun, is often attributed to perfectly encapsulating the feeling of summer and never wanting it to end.
After singing it a couple of times, you really start to feel summer even in the dead of either the rainy or dry season. But out of curiosity (and maybe after becoming bored with the song), you start to wonder, “Can the sun actually appear during midnight?”
If you actually listened to your elementary science teacher, you’d know the answer to that question is a resounding yes. Let’s break it down a bit more.
As the Earth rotates around the sun, it does so at an angle of around 23.5°. Because of this slight tilt, different parts of the Earth’s surface receive different amounts of sunlight. This tilt also explains why the current season in the Northern Hemisphere, or the northern half of the earth with respect to the equator, is directly opposite the season in the Southern Hemisphere.
From June to August, the Northern Hemisphere is tilted towards the sun and receives more sunlight compared to the Southern Hemisphere. This also means that the Northern Hemisphere experiences summer as the sun heats a larger area of the Northern Hemisphere. Countries near the equator experience less drastic temperature changes because the equator receives roughly equal amounts of insolation throughout the year. However, countries farther from the equator may experience more drastic changes in temperature and daylight hours. For example, during the winter, the United Kingdom experiences only seven to eight hours of daylight daily; however, during the summer, it experiences more than 17-18 hours of daylight because of the Earth’s tilt.
Now, it is precisely because of this tilt that we can experience the midnight sun.
The polar regions of our Earth experience the most drastic changes in sunlight. From March 21 to September 23, the Arctic Circle experiences 24-hour daylight, hence the term “midnight sun.” The opposite is also true in the Antarctic Circle, wherein the Antarctic experiences never-ending darkness for roughly six months. Then, the Antarctic experiences the midnight sun for another six months, and the Arctic Circle experiences darkness for another six months, and so on.
This tilt, which causes our seasons, is also not constant, meaning our seasons continue to change despite it seeming so permanent. Through what we call the Milankovitch cycles, Earth’s tilt and orbit directly determine our climate and the future of seasons.
First, we need to understand that the Earth’s orbit is not perfectly circular, but elliptical. Because of this, during July and January, the distance between the Earth and the Sun changes, and thus also the amount of sunlight the Earth receives. During January, the Earth is at its closest to the sun at around 147 million kilometers away during a phenomenon called perihelion. On the other hand, during July, the Earth is at its farthest from the sun at around 150 million kilometers during the phenomenon called aphelion. As it turns out, the distances of both the perihelion and aphelion are not constant, but differ ever so slightly as time passes. The changes in the Earth’s orbit are called its eccentricity, which happens roughly every 100,000 years. Because of this, the Earth’s perihelion and aphelion also drastically change, increasing or decreasing the heat from the Sun.
Next is the Earth’s tilt. Currently, the Earth’s tilt is at 23.5°; however, this also varies between 22° and 24.5°. The more drastic the Earth’s tilt, the more intense seasons become.
And finally, we have the Earth’s precession. While the Earth spins on its axis, it does so through an axial movement, like how a spinning top slowly wobbles before coming to a complete stop. Because of this, the severity of the seasons in each hemisphere differs and affects the timing of each season.
If the tilt of the Earth were a few degrees less, the midnight sun might still happen, but summer would cease to exist. With less tilt, summers lose their intensity, no longer bringing enough heat and sunlight to undo the cold built up during the winter.
As the Milankovitch cycles overlap with one another, more drastic changes within our climate and seasons begin to occur and produce what we call ice ages. These ice ages are not sudden, but slow transformations occurring through the Milankovitch cycles. As the Earth’s tilt becomes smaller, alongside the changes in eccentricity and precession, the summers don’t completely melt all ice from the previous winter. Over the years, this ice accumulates, forming massive ice sheets and glaciers that reflect sunlight back into space, causing further cooling in a continuous cycle. Scientists have also told us that we are currently in between ice ages right now. These periods are called the interglacial periods, which last roughly around 10,000 years and begin to signal the next, upcoming ice age.
And so, the same tilt that gave us Zara Larsson’s midnight sun and that feeling of a never-ending summer is part of a larger system, one that can slowly remove summer itself. Because one day, far in the future, the sun may still hang above the horizon at midnight, but it might not be enough to melt the winter.
Sources:
https://phys.org/news/2014-11-earth-orbit-sun.html
https://www.universetoday.com/articles/milankovitch-cycle
https://earthsky.org/tonight/earth-comes-closest-to-sun-every-year-in-early-january/
