Spring has officially arrived, marking the start of a new season for the Northern Hemisphere and the beginning of autumn in the Southern Hemisphere. The vernal equinox, which falls on Thursday, brings the sun directly overhead at noon, illuminating both the north and south poles simultaneously.
The equinox is a significant event that has been celebrated by cultures around the world for centuries. Nowruz, the Iranian New Year, is based on this spring equinox. In Mexico, people gather at the Mayan site Chichen Itza to witness the sun casting a serpent-like shadow pattern on El Castillo during the equinox.
So, what causes the Earth’s orbit? As our planet travels around the sun, its axis tilts either towards or away from the sun. This results in unequal amounts of sunlight falling on the northern and southern halves of the planet. During an equinox, the Earth’s axis aligns with its orbit, resulting in equal sunlight for both hemispheres.
The word “equinox” comes from two Latin words meaning “equal” and “night,” reflecting the nearly equal day and night lengths during this time. The Northern Hemisphere’s spring equinox typically falls between March 19 and 21, while its autumnal equinox occurs between Sept. 21 and 24.
In contrast, the solstices mark the times when the Earth is at its most extreme tilt towards or away from the sun. This leads to unequal day and night lengths. The Northern Hemisphere’s summer solstice falls between June 20 and 22, resulting in the longest day and shortest night of the year. Conversely, the winter solstice occurs between December 20 and 23.
There are also two ways to divide the year: astronomical seasons and meteorological seasons. Astronomical seasons depend on the Earth’s orbit around the sun, while meteorological seasons are defined by temperature cycles and break down the year into three-month periods. The former typically aligns with the solstices, while the latter starts in March, June, September, and December.
Source: https://www.pbs.org/newshour/science/its-the-spring-equinox-what-in-the-heavens-is-happening