What are the reasons why December 13th is the shortest day

As we approach the winter season, the days become progressively shorter, with December 21st marking the official winter solstice, the shortest day of the year. However, interestingly, December 13th is often considered the shortest day in many parts of the world. What are the reasons behind this phenomenon? Let’s delve deeper into the science of it.

The Earth’s axial tilt is the primary factor responsible for the variation in daylight throughout the year. December 21st is known as the winter solstice because it marks the moment when the Northern Hemisphere is tilted farthest from the sun. However, it takes a few days for this effect to become noticeable, resulting in December 13th being perceived as the shortest day.

One of the contributing factors to the brevity of daylight on December 13th is the Earth’s elliptical orbit. Our planet follows a slightly oblong path around the sun, causing variations in the distance between the two bodies throughout the year. Around December, the Earth is at its closest point to the sun, known as perihelion. Surprisingly, being nearer to the sun does not result in longer days. This is because the axial tilt is the primary determinant of day length, overriding the impact of the Earth’s proximity to the sun.

In addition to the Earth’s elliptical orbit, the phenomenon of atmospheric refraction also plays a role in the perceived shortness of the day on December 13th. When sunlight enters the Earth’s atmosphere, it undergoes refraction – bending as it passes through the layers of gases. This bending effect causes the sun to appear higher in the sky than it actually is.

As a result, even though the actual duration of daylight on December 13th may not be significantly shorter than the surrounding days, the perceived length of the day is shortened due to the sun’s apparent higher position. This can create the illusion of a shorter day, leading to the misconception that December 13th is indeed the shortest day.

While December 21st remains the official day of the winter solstice, December 13th being considered the shortest day has cultural significance in various regions around the world. Festivals and celebrations, such as Saint Lucia’s Day in Scandinavia, are observed on this date to mark the transition into the winter season. These traditions have been carried on for generations, reinforcing the belief that December 13th is the shortest day.

In conclusion, although December 21st is scientifically recognized as the winter solstice, December 13th is often perceived as the shortest day due to the combined effects of the Earth’s axial tilt, its elliptical orbit, and atmospheric refraction. While the actual duration of daylight may be similar to the surrounding days, the apparent position of the sun in the sky creates the illusion of shorter daylight hours. So, as we experience the winter season and the darkness seems to grow, let us remember the fascinating science behind why December 13th is often regarded as the shortest day.