September Equinox

   

The near-equinox taken from a Sunlight APP
half a day later. (screenshot) See the equal block
of night, instead of that wave-like darkness? 

  As fall moves around the corner, a very important date is to remember. September 22-23, is the September Equinox, where both North and South Hemisphere gets the same amount of sunlight and nighttime. This marks the beginning of the transition of seasons, for the North, its fall, the south, its spring. The 2018 autumn equinox happens September 22 at 6:54 PM (Pacific Time Zone). Hanneke describes, "On Sept. 22 [2018] at 9:54 p.m. EDT (01:54 GMT on Sept. 23), the sun will cross the celestial equator, or an imaginary line that projects Earth's equator into space. At this exact moment, the Northern and Southern hemispheres will receive an equal amount of sunshine, and the length of day and night will be approximately equal around the world — hence the term 'equinox', which is derived from the Latin phrase meaning 'equal night'." This event happens on this time, perfectly when the Sun meets the Earth's equator, thus the equinox or equal night happens.

Earth's Phases in late 2010 and 2011, see the March and
September Equinox (right), and the phases
summer and winter (left). Courtesy of Space.com

   However, sometimes the dates may land on Sep 20-24 because of the uneven dates of an year, so that is why there is a leap year every four years, to keep the season equal every year. Despite, a leap year can still cause the equinox to fall on other dates, but not too far from the average date. Hanneke adds on, "The last time the autumnal equinox fell on Sept. 21 was over a thousand years ago, and the last Sept. 24 equinox was in 1931, according to timeanddate.com. While it's been a long time since the equinox occurred on Sept. 21, we can expect to see it happen twice in the next century, first in 2092 and then in 2096. The next Sept. 24 equinox will be in the year 2303. (Keep in mind that these dates are based on Universal Time, so some time zones may not experience these equinoxes on the dates listed here.)" This means that equinoxes that happened on the two outsider dates are pretty uncommon and happens only in thousands of years. Universal Time is seven hours ahead of Pacific Time (extra note).


Bibliography:

Weitering, Hanneke. "Why the Autumn Equinox Doesn't Fall on the Same Day Every Year" September 22, 2018. Space.com. Retrieved on September 23, 2018 from:
https://www.space.com/41910-autumn-equinox-2018-later-than-usual.html/.