‘Tis the season for cooler temperatures, pumpkin spice lattes and all things fall. Let’s talk a little bit about the science behind the day that makes this season so great.
First, let’s talk about the start of fall.
In 2021 Fall will begin on Wednesday, September 22 at 3:20 PM EDT. This is the exact moment that the sun’s rays will be over the equator, this happens at the exact same time all across the globe just in different time zones. The sun will be moving from north to south heading towards the southern hemisphere as they prepare for the start of spring and eventually summer.
This is also the day that the sun will rise exactly due east and set exactly due west for mainly everyone except for those living at the north and south poles. This happens due to the sun moving on the celestial equator which is an imaginary line above the actual equator, if you were to look up at noon the sun would appear directly overhead, this only happens for both the spring and autumn equinox.
Equal days and nights:
Equinox is Latin for equal and night so you can expect close to 12 hours of daylight and 12 hours of night. The reason this happens all has to do with the way the earth is tilted.
First, we know that the Earth is tilted on its axis at 23.5 degrees. During a solstice, the tilt of the axis will either point towards or away from the sun. This means that the northern and southern hemispheres trade when they receive the sun’s light and warmth directly. During an equinox, the Earth’s tilt and even orbit combine in a way that the axis doesn’t exactly tilt away from or toward the sun. Thus the days and nights are somewhat equal but maybe a few minutes off.
Where do we go from here:
From here our days will become shorter and our nights will become longer. The loss of daylight will continue until we head towards the winter solstice, this is the day that the tilt of the axis will be away from the sun in the northern hemisphere. This will mark the shortest day of the year or the longest day of the year in the southern hemisphere.
The first day of winter will be Tuesday, December 21st 2021.