On Monday, March 20, 2023, the northern hemisphere experiences the Spring Equinox, which marks the first day of spring. This occurs when the Sun crosses the celestial equator, moving from the southern hemisphere to the northern hemisphere. The equinox is called ‘equal night’ because it signifies the point in time when day and night are almost equal in both hemispheres.
More Sunlight Than Darkness
During the Spring Equinox, we get a few more minutes of sunlight, thanks to atmospheric refraction that bends the Sun’s rays, causing the Sun to appear above the horizon when it’s actually below. It results in slightly more daylight than darkness. While the equinox lasts only for a moment, it’s an important event for astronomers, meteorologists, and people who want to mark the start of spring.
First Point of Aries
The exact point at which the Sun crosses the celestial equator during the spring equinox is called the First Point of Aries. It was named by the Greek astronomer Hipparchus in 130 BCE, when it was located in the Aries constellation. However, due to precession, which causes the direction of the Earth’s axis to change direction, the First Point of Aries now lies in the Pisces constellation. It is slowly moving towards the Aquarius constellation at a rate of one degree every 70 years. By the year 2597, the First Point of Aries will be located in Aquarius, and it will take another 23,000 years for it to return home to its namesake.
Two Ways to Define Spring
Astronomical spring and meteorological spring are two ways of defining the start of spring. Astronomical spring is based on the position of the Earth in its orbit around the Sun and begins on the vernal equinox (March 20 in the northern hemisphere), when the Sun is directly above the equator, making day and night almost equal in length. Meteorological spring, on the other hand, is defined as the months of March, April, and May in the northern hemisphere, and September, October, and November in the southern hemisphere. This definition is based on the annual temperature cycle and is used by meteorologists for easier comparison of seasonal statistics.
