The equinox is a wonderful astronomical phenomenon that has many meanings and aspects. It is a time of changing seasons, the balance between day and night, observing the sky and nature, culture and history, magic and fortune-telling, celebration and fun. It’s also an opportunity to learn interesting facts and stories about the vernal equinox. The next equinox will be on Saturday, September 23.
The equinox is the moment when the Sun is directly above the Earth’s equator, the line that divides our planet into two equal halves. So day and night are the same length all over the world. The equinox occurs twice a year: in March and September. We call March the vernal equinox, and September the autumnal equinox. Depending on which hemisphere we live in, the equinox marks the beginning of spring or fall.
The equinox occurs twice a year:
- March 20/21 – The Sun passes through Aries, the vernal equinox occurs in the Northern Hemisphere, and the autumnal equinox occurs in the Southern Hemisphere.
- September 22/23 – The Sun passes through the point of Libra, the autumnal equinox occurs in the Northern Hemisphere, and the vernal equinox occurs in the Southern Hemisphere.
The dates and times of the equinoxes are not fixed because the Earth year (the time the Earth revolves around the Sun) is not exactly 365 days long. So, every four years we have a leap year, which has 366 days and corrects this difference. In addition, the date of the equinox is affected by the precession of the Earth’s axis (a slow change in the direction of the Earth’s rotation axis), causing the equinox points to move along the ecliptic.
You can find more interesting facts about the Sun and Earth on the spider’s web:
But why does this happen? To understand this, we need to know that the Earth does not revolve around the Sun exactly perpendicular to its axis, but is slightly tilted. This tilt is about 23.5 degrees and causes the Sun to illuminate the Earth from different angles at different times of the year. When the Earth is closest to the Sun (in January), the Southern Hemisphere faces more toward the Sun and has summer, while the Northern Hemisphere has winter. When the Earth is furthest from the Sun (in July), the opposite is true.
The equinox is the moment when the Earth is exactly in the middle between these two extreme positions. Then the sun rises perpendicular to the plane of the equator and illuminates both hemispheres equally. So day and night are the same length all over the world, because every point on Earth is illuminated and shaded by the sun for the same amount of time.
What happens in moderation?
During the equinox, the length of day and night is equal across the Earth. This means that the center of the sun’s disk lies above the horizon for the same amount of time as it lies below it. Moreover, the sun rises exactly in the east and sets in the west.
However, the length of day and night is not exactly equal. This is due to several factors:
- Angular size of the Sun – the size of the Sun that appears to us in the sky. The larger the Sun, the longer it is visible above the horizon.
- Refraction – the refraction of sunlight by the Earth’s atmosphere. Thanks to this, we can still see the sun for a while after it drops below the horizon.
- Geographical location – i.e. latitude and longitude of the monitoring location. The further we are from the equator, the greater the difference between the length of day and night.
For these reasons, the day lasts slightly longer than the 12 hours on the day of the vernal equinox (for example in Warsaw by about 9 minutes and 30 seconds).
During the equinox, the angle at which the sun’s rays strike the Earth also changes. On the day of the equinox, the sun’s rays fall perpendicular to the equator, and the farther away they are from it, the greater their inclination to the Earth’s surface. This affects the temperature and climate at different latitudes.
How to monitor moderation?
There are several ways to monitor moderation. First: We should note that the sun rises completely in the east and sets completely in the west. This means that the horizon line divides the solar disk into two equal parts. Another method is to measure the height of the sun above the horizon at noon. On the day of the equinox, this height is equal to 90 degrees minus the latitude of the observation location. For example, in Warsaw, which is located at 52 degrees north latitude, the sun’s altitude is 38 degrees.
Another way is to pay attention to changes in nature associated with the seasons. On the day of the vernal equinox, you can notice plants and animals returning to life after their winter dormancy. Birds return from warm countries, flowers bloom, and the air temperature rises. On the day of the autumnal equinox, you can observe plants and animals preparing for winter rest. Leaves change color and fall from trees, birds fly away to warm countries, and the air temperature drops.
Interesting facts about moderation
The equinox is not only an astronomical phenomenon, but also a cultural and historical phenomenon. Here are some interesting facts about moderation:
- On the day of the equinox, you can easily calculate your latitude. Simply measure the height of the rising sun (in degrees) and subtract it from 90 degrees. If the sun was on the south side of the sky, our latitude was north (N), and if it was on the north side, our latitude was south (S).
- The vernal equinox was an important reference point for many ancient civilizations, whose calendars and holidays were based on it. For example, the Egyptians built the pyramids so that the sun would shine directly between the two pyramids at Giza on the equinox. The Maya civilization observed the phenomenon of the “descent of the snake” on the Kukulkan Pyramid in the city of Chichen Itza, where the shadow of the stairs created the illusion of a moving snake.
- The equinox is also a magical time filled with superstition and prophecy. Many peoples believed that it was possible to communicate with the dead, heal diseases, predict the future or find hidden treasures. Some of these customs have survived to this day, such as lighting fires, planting trees, or collecting herbs.
- The moderation is also an opportunity to celebrate and have fun. Many countries organize temperance-related festivals, concerts, cruises, outings and workshops. For example, Warsaw hosts the Vistula Equinox, where you can enjoy a panoramic view of the city from the deck, listen to live music or relax on the beach.
- Moderation is also an inspiration for many artists and creatives. For example, writer Neil Gaiman wrote the story “Equinox,” in which he describes the main character’s encounter with a mysterious woman during the autumnal equinox. Composer Jean-Michael Jarre composed “Equinoxe”, a musical interpretation of the change of seasons at the equinox.
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