Equinoxes, Solstices, and Why We Have Seasons

Something very special is happening on March 20th, 2021. It is the day of the Spring Equinox (also known as the first day of Spring, and the Vernal Equinox), which means that we should be done with old man winter (I can't make any promises on that though), and be ready to usher in the season of life. Plants will begin blooming, trees will begin budding out, and young animals will start appearing in our little piece of coastal paradise. It is one of the more joyous times of the year.

To help explain why the Spring Equinox is so significant from a scientific perspective, it helps to understand why we have seasons on Earth. The seasons on Earth change quarterly because the planet is slightly tilted on its axis as it completes its annual orbit around the Sun. This means that different points on Earth receive varying levels of sunlight at different times of year. If the Earth was not tilted, the Sun would always appear to be located directly above the Equator. Therefore, the amount of light that a given location receives would be fixed. As a result, there would be no seasons. Every place would stay the same all year long. The Sun would rise and set at the same times every day. The weather would presumably be relatively stable, meaning some locations would be in a permanent freeze and others in a never ending heat wave. And some would be in a constant flood or an endless drought. That’s not sustainable for supporting human life. So we need the four seasons to help make all of Earth habitable and not just the places that would be lucky enough to have less extreme conditions. I wouldn't want to speculate too much about what conditions Ocean Shores would experience in such an environment since it doesn't exist. However, given that there always seems to be a breeze in Ocean Shores, it may be safe to assume that it would be an even windier place than it is now.

Now that you know why we have seasons on Earth, let's look at why the Spring Equinox is so important. The Spring Equinox marks the point when the Sun crosses the path of the equator, and becomes positioned precisely above the equator between the Northern and Southern Hemispheres. During the Spring Equinox, there will be approximately the same number of hours of daylight and nighttime. Since there are twenty-fours in a day, that means there will be twelve hours of daylight and twelve hours of nighttime. This is evident in the word Equinox's origin. It is derived from the Latin words equi (which means 'equal') and nox (which means 'night'). Once we pass the Spring Equinox, there will be more daylight and less nighttime until September 22nd, 2021. That is when the Autumn Equinox will occur. The Sun will be crossing the equator again, and will be positioned precisely above the equator between the Northern and Southern Hemispheres, just like it does during the Spring Equinox. There will also be equal amounts of daylight and nighttime again before we descended into Autumn and Winter when darkness prevails and the Sun only has about eight hours a day to shine (when it can get through the clouds, that is).

It is worth noting that, on the day of an Equinox, the length of day and night are not exactly equal. The reason for this is because the Sun appears as a disk in the sky, and the top half makes its way above the horizon before the center. Additionally, this sunlight is refracted by the Earth's atmosphere. Therefore, the Sun appears to rise before its center at the horizon, which gives you an additional ten minutes of daylight. The day in which day and night are truly equal is known as the Equilux. It occurs a few days before the Spring Equinox, and a few days after the Autumn Equinox. For Ocean Shores, those dates are March 16th, 2021, and September 24th, 2021.

Now you may be wondering why I haven't mentioned a summer equinox or a winter equinox yet. Well, that is because they don't exist. Instead, we have a Summer Solstice and a Winter Solstice. These take place when the Sun’s path in the sky is as far from the Equator as it is going to get. The Summer Solstice, which occurs on June 20th, 2021, is the day which has more daylight than any other for the Northern Hemisphere. In Ocean Shores, we'll have fifteen hours, fifty-three minutes, and forty-one seconds of daylight on that day. Other places will have even more. That is because the Sun will be at its highest point of the year. The Northern Hemisphere of Earth will be tilted towards the Sun, which will lead to more sunlight and warmer temperatures. The Sun's powerful rays will be directly over The Tropic of Cancer. In places that are closer to the North Pole, such as Alaska, Iceland, and Norway, this can lead to near continuous daylight. Of course, they'll have to make up for it at the Winter Solstice, which will occur on December 21st, 2021, with near continuous darkness. In Ocean Shores, we won't suffer through a day of total darkness. Instead, we'll have eight hours, thirty minutes, and fifty-four seconds for the Sun to shine. At the Winter Solstice, the Sun will be at lowest point of the year, and the Northern Hemisphere will be tilted away from it, which will lead to less sunlight and colder temperatures. The Sun's powerful rays will be directly over The Tropic of Capricorn, which will be the longest day of the year for our friends in the Southern Hemisphere.

We hope you enjoyed this discussion on Equinoxes, Solstices, and Why We Have Seasons. We threw a lot of dates at you today, so we'll end with a recap of them all so you can mark your calendars and enjoy the equinoxes, solstices, and equiluxes that 2021 will bring. Thanks for reading!

The equinoxes, solstices, and equiluxes of 2021 (March to December)

• March 16th: Spring Equilux - equal amount of day and night
• March 20th: Spring Equinox - slightly more day than night
• June 20th: Summer Solstice - longest day and shortest night of the year
• September 22nd: Autumn Equinox - slightly more day than night
• September 24th: Autumn Equilux - equal amount of day and night
• December 21st: Winter Solstice - shortest day and longest night of the year

References

1. https://www.metoffice.gov.uk/weather/learn-about/weather/seasons/equinox-and-solstice
2. https://www.britannica.com/story/whats-the-difference-between-a-solstice-and-an-equinox
3. https://sunrise-sunset.org/us/ocean-shores-wa

© Ian D. Caldwell, March 2021