Do you know that our Earth actually rotates on a tilted axis? Earth rotates by itself around a fixed axis called the rotational axis. At the same time, Earth also orbits around the Sun in a fixed axis called the orbital axis. The rotational axis is not actually perpendicular to the orbital axis. As the result, our Earth is tilted to a certain angle compared to its orbital axis. And the celestial equator, the imaginary line in the sky above Earth’s equator, is also tilted to a certain angle compared to Earth’s orbital axis.
Equinox is the time when Earth’s rotational axis is rather perpendicular to the Sun’s rays, and the Sun crosses the celestial equator from south to north. At equinox, the solar terminator or the edge between night and day is perpendicular to the equator. As a result, the northern hemispheres and the southern hemispheres are equally illuminated and the length of day and night are nearly equal in every part of the world. Equinox comes from the Latin word “equi” meaning equal and “nox” meaning night.
Equinox occurs twice a year, around 20 March and 23 September. This year, March equinox will be at 21 March. March equinox is called vernal (spring) equinox in the northern hemispheres and autumnal equinox in the southern hemispheres. As the name suggests, March equinox marks the start of spring in the northern hemispheres and the autumn in the southern hemispheres. March equinox is often used by astronomers to measure a tropical year, which is the mean time it takes for Earth to complete a single orbit around the Sun. March equinox also has long been celebrated as a time of rebirth in the northern hemisphere.
If you are in the equator, you could celebrate March equinox by watching the shadows disappear on Noon. You could also celebrate it by bringing spring into your home, either by planting a new flower or plant, or decorating your house with spring flowers and decorations. You could also gather with families or friends around a bonfire and play music, dance, sing, and tell stories. Or you could simply start something new!
How about you? Tell us your favorite March equinox activity, or share your most memorable March equinox celebration!