The Spring equinox of 2024, occurring on March 19th, signifies the onset of spring in the Northern Hemisphere and the commencement of autumn in the Southern Hemisphere. This event also heralds a rare occurrence known as “equal night” across the globe. As of tonight, the Northern Hemisphere officially enters the spring season.
March 19th marks the occurrence of the March equinox, an annual astronomical phenomenon symbolizing the transition of seasons worldwide. In the Northern Hemisphere, this equinox denotes the conclusion of winter and the commencement of spring, hence its alternative name, the vernal equinox or spring equinox. Conversely, in the Southern Hemisphere, it signifies the conclusion of summer and the onset of autumn.
The term “equinox” originates from Latin, meaning “equal night.” This is because during this period, as well as several days preceding and following it, the duration of daylight is nearly identical, approximately 12 hours, in both hemispheres. However, slight variations exist depending on one’s proximity to the equator, as noted by the National Weather Service.
Equinoxes occur biannually, in March and September, owing to the tilt of the Earth’s axis. The Earth orbits the sun at an inclination of about 23.5 degrees, resulting in differential sunlight exposure across the planet throughout the year. For instance, during the summer solstice in June, the Northern Hemisphere tilts toward the sun, receiving maximal sunlight and thereby experiencing the longest day of the year, while the Southern Hemisphere tilts away, leading to its longest night.
During equinoxes, however, the Earth’s tilt aligns with its orbit, causing the sun to be directly positioned over the equator rather than to the north or south. Consequently, this alignment results in “equal night” in both hemispheres, a phenomenon that is prominently observable from space, as depicted in striking photographs.