Equinox: The Light and Darkness Phenomenon That Happens Twice a Year

Twice a year, in March and September, the amount of daylight and darkness are "nearly" the same length at all latitudes. From the Latin words "aequus," which means equal, and "nox," which means night, this phenomenon is called the equinox.

What Happens During the Equinox

The amount of sunlight or radiation each part of the Earth at different times of the year gets depends on its position in its orbit. The planet tilts about 23.5 degrees, meaning different parts of the planet do not get an equal amount of sunlight.

It is widely known that the Sun rises from the East and sets to the West. But for half of the year, the Sun moves north and then moves south for another half. For instance, the North Hemisphere experiences longer days than nights in July than the Southern hemisphere.

The opposite happens in December as the Southern hemisphere sees more daylight hours, and the Northern hemisphere has fewer.

But in March and September, the National Oceanic and Atmospheric Association said that the Earth's tilt aligns with the orbit around the Sun, and it does not appear to tilt with respect to the Sun.

That means the Sun sits directly above the equator, and both the Northern and Southern hemispheres got the same amount of daylight and night. The line that divides the day and night called "gray line" or the "twilight zone," divides the Earth and runs through the north and south poles during these times of the year.

During an equinox, the Earth experiences lesser sunlight because sunrise happens when the tip of the Sun edges over the horizon. For several days before and after the equinox, the Earth will experience a day for a few minutes more than 12 hours.

When Does Equinox Happen?

Equinoxes do not necessarily happen at the exact date every year. They usually occur around or on March 20 and September 23. These changes happen because the number of days in a year is not exactly 365 days; six hours accumulate each year.

The equinox signals the beginning of spring or autumn. For the northern hemisphere, the equinox in March signals the beginning of spring and is referred to as the vernal equinox or the spring equinox.

At the same time, the Southern hemisphere shifts into autumn equinox. The same is true during the September equinox when the northern hemisphere enters the cold months of the year, and the southern hemisphere enters spring.

How Was the Equinox Discovered?

For thousands of years, people have been tracking the Sun's movements, often incorporating the equinoxes with traditions. Many ancient civilizations see these as the start of a new season and signal the time for planting and harvesting crops.

According to the Coto Japanese Academy, Japan celebrates both the equinoxes in public holidays to remember and worship their ancestors and loved ones.

Ancient monuments and markings were also made to mark the equinoxes, just like the Hindu temple Angkor Wat in Cambodia which was built between 1113 and 11150 A.D. The temple is considered to be the largest religious monument in the world. Scientists have published accounts of astronomical links between the temple's architecture and celestial events.

Also, the Mayan temple in Mexico, known as Temple of Kukulcan dedicated to a serpent god. During the equinox, the serpent looks like it descends the temple's side and travels down to the underworld, thanks to a trick by the light.