On Thursday, September 22, 2016, at precisely 10:21 a.m. EDT, the Sun will cross the Equator, marking the precise moment of the Autumnal Equinox, or the first official beginning of fall.
So what does that mean? Essentially, our hours of daylight — the period of time each day between sunrise and sunset — have been growing slightly shorter each day since the Summer Solstice on June 20th, which was the longest day of the year in 2016 (at least in terms of daylight). Even after three months of the days growing shorter, we were still seeing more light than darkness over the course of a day. The Autumnal Equinox marks the turning point, when darkness begins to win out over daylight but on the 22nd, the days and nights are approximately equal in length. The word equinoxcomes from the Latin aequus(equal) and nox (night).
So now, for the next three months, our hours of daylight will continue to grow shorter. In December (December 21, 2016, at 5:44 a.m. EST, to be exact), we welcome the Winter Solstice, the shortest day of the year in terms of hours of daylight.
After the Winter Solstice, the days will begin to grow longer again. It will take another three months, until the Vernal (Spring) Equinox (March 20, 2017, at 6:29 a.m. EDT), for the periods of daylight and darkness to reach equilibrium once again.
From the Vernal Equinox, the days will continue to grow longer, until we reach the Summer Solstice again on June 21, 2017, at 12:24 a.m., EDT, and the cycle starts all over again!
Did you ever wonder…
Why doesn’t the change of seasons happen at the same time every year? Well, to explain, the Earth takes approximately 365.25 days to make one trip around the Sun. This is why we have a leap year every 4 years, to add another day to our calendar to make up for that .25 day, so that there is not a gradual drift of dates through the seasons. For the same reason the exact time of the equinoxes and solstices are not the same each year, and generally will occur about 6 hours later each year, with a jump of a day backwards on leap years.
Why doesn’t the change of seasons happen at the same time every year? Well, to explain, the Earth takes approximately 365.25 days to make one trip around the Sun. This is why we have a leap year every 4 years, to add another day to our calendar to make up for that .25 day, so that there is not a gradual drift of dates through the seasons. For the same reason the exact time of the equinoxes and solstices are not the same each year, and generally will occur about 6 hours later each year, with a jump of a day backwards on leap years.
So no matter what the weather is doing outside your window on the 22nd, this day marks the official start of autumn, and with it, we’ll see the many changes this new season brings, including the leaves changing color!
By The Farmers' Almanac Staff
No comments:
Post a Comment