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, September equinox will be at 23 September 2019. September equinox is called autumnal equinox in the Northern Hemispheres and vernal equinox in the Southern Hemispheres. The September equinox may be taken to mark the end of summer and the beginning of autumn (autumnal equinox) in the Northern Hemisphere, while marking the end of winter and the start of spring (vernal equinox) in the Southern Hemisphere.

Celebrate autumnal equinox by staying up during the night to welcome autumn. You could also create fall-inspired craft, or plant some crops that will produce during fall or even into winter, such as cauliflower, lettuce, red beet, radishes and shallots. You could also take the time to contemplate your life and find balance, as autumn is a season when the buzzing activity of summer dies down and the excitement of life outdoors begins to relax into the more evenly paced, more predictable rhythm of fall.

How about you? Tell us your favorite September equinox activity, or share your most memorable September equinox celebration!