Summer Solstice: Why Today Feels Like the Longest Day of the Year
When I ask someone, “How was your day?”, they often respond that “It felt long.” Sometimes, if it was a really tough day, they will go as far as claiming that it felt like “the longest day of the year.” On most days, 364 to be precise, that claim is factually false. Today, however, anyone in the northern hemisphere can correctly state that this feels like the longest day of the year.
That’s because today is the Summer Solstice, which means that today the Earth is tilted directly towards the Sun. In other words, because the Earth’s axis of rotation (the skewer around which the Earth spins) is not perpendicular to the plane of its orbit (the elliptical made by its yearly ring around the Sun), the Earth spends half of the year tilted towards the sun, and half of the year tilted away from it. Today, the northern hemisphere’s tilt is directed straight at the Sun. As a result, the northern hemisphere experiences its longest day of the year.
The Earth is always tilted in the same direction as it orbits the sun. As a result, the northern hemisphere faces the sun more directly for half of the year, and the southern hemisphere faces it more directly for the other half of the year. This causes the seasons, solstices, and equinoxes. It is also the reason why days have different lengths. Image: PeterHermesFurian/iStock/Thinkstock
This all began around 4.51 billion years ago, when a planetoid called Theia collided with the molten mass that was our infant Earth. While the exact details of the collision are still debated, scientists agree that the impact created our moon and left the Earth with an axis of rotation tilted 23.5° to the side. One consequence of this planetary fender-bender was the four seasons. They occur by the same logic as the solstices.
When the northern hemisphere leans towards the Sun, sunlight has less atmosphere to pass through on its way to Earth, so the northern hemisphere absorbs more energy. This raises the temperature and, for 3 months, everywhere north of the equator experiences summer. Simultaneously, the southern hemisphere is leaning away from the Sun, and therefore absorbing less energy. That’s why places below the equator are experiencing winter right now.
Fast forward 6 months and this switches. The northern hemisphere will get less sunlight, less energy, and therefore, experience winter. Meanwhile, the southern hemisphere will get more exposure to the Sun’s rays, and subsequently, experience its summer.
The amount of daylight you experience during the solstice depends on what latitude you are at (your distance from the equator). For penguins in Antarctica, today will be completely dark. For the polar bears around the North Pole, today will be sunny all day! How many hours of daylight will you get today? Image: PeterHermesFurian/iStock/Thinkstock
So, our planet’s unique tilt causes us to experience four different seasons. Summer when a hemisphere tilts towards the Sun; fall when it has orbited 90°; winter when the hemisphere tilts away from the Sun; and spring when it has orbited another 90°. The full cycle takes just over 365 days to complete, and causes the variance in daylight that makes some days, like today, longer than others!
Be Thankful for Long Days
With that in mind, it’s worth considering what the Earth could be like if it didn’t have seasons and differing day lengths. This might well have been the case had that 4.51 billion year old celestial collision never occurred. Some scientists believe that the Earth might have retained a more acute angle of axial tilt, like Mercury’s, which is only 2.11°. The result would be a permanently consistent amount of daylight, hardly-recognizable seasons (if any), and a very different web of life.
Mercury, the closest planet to the Sun, has a very small axial tilt angle. As a result, ‘days’ are always the same length, and there is no seasonal variation in the climate. This is one of many reasons that lifeforms like the ones on Earth could never exist on Mercury. Image: FlashMyPixel/iStock/Thinkstock
That’s because the ancestors of every living organism on Earth evolved under specific conditions in a particular environment. If those conditions had been different, the environmental pressures would have been too, and life on Earth would not look the way it does today. That’s assuming that life would have appeared at all, however, because without the near-perfect climate of our current Earth, there’s no certainty of that happening.
Where exactly the hereditary information in every living cell originated is still unknown, but many scientists believe that the first DNA formed because of the exact conditions present on the early Earth. If the Earth’s tilt hadn’t been 23.5°, its environment would have been substantially different, and it’s possible that life as we know it may never have begun. Image: cosmin4000/iStock/Thinkstock
Of course, this is all speculation, but its value lies in giving us the gift of gratitude. One of the best things science does is enable us to view the world with new eyes, to be amazed by it all, and to appreciate our own existence as the miracle it truly is. In this case, understanding how and why day lengths differ, and seasons occur, can help us appreciate all days, be they long or short.
If you need some more reasons to be thankful, today is also an international day of celebration, with festivals occurring throughout the northern hemisphere in celebration of the Summer Solstice. In New York City, June 21st is a day full of music, with hundreds of free music concerts occurring around the city from sunrise until sunset. In Norway, they celebrate the start of summer with Slinningsbålet, a flaming festival that broke the world record for “largest bonfire” in 2016.
Regardless of whether you celebrate today by rocking out, sitting by the fire, or just spending a few more minutes soaking up some extra sun, make sure to appreciate it! In the words of Olympic sprinter Wilma Rudolf, “When the sun is shining I can do anything; no mountain is too high, no trouble too difficult to overcome.”
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