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Jeremy Kappell

Fall "officially" begins tomorrow, but WHY?

Although it's been feeling a lot like fall for several days now, autumn officially begins tomorrow.

The astronomical start to the fall season arrives at precisely 9:30 am ET Tuesday morning with the Autumnal Equinox, also known as the Fall Equinox.

But what occurs at that exact moment to mark the new season?

The word equinox comes from the Latin words for "equal night." The fall and spring equinoxes are the only days of the year in which the Sun crosses the celestial equator.  

The equinox occurs on the moment  that the sun's most direct rays move from the Northern Hemisphere and into the Southern Hemisphere.  It is at that moment that the sun's rays are pointed directly over the equator.


You see, the earth revolves with a constant 23 1/2° tilt with respect to the alignment of the poles with the orbiting plane around the sun.  

As the earth travels around the sun, the sun's most direct rays shifts across the face of the earth.

It is during the spring and summer months that these direct rays of the sun are pointed towards the Northern Hemisphere and away from the Southern Hemisphere (their cold season).  

By September these direct rays shift to the south, and on the Fall Equinox, tomorrow, align themselves along the equator as the entire planet experiences nearly equal parts day and night.

The shift away from the sun will continue for the Northern Hemisphere until the start of winter during the Winter Solstice on December 21st, also the shortest day of the year.  

By the time winter arrives we will experience only about 9 hours of daylight and around 15 hours of darkness!  

So why aren't there exactly 12 hours of daylight and darkness on the equinox?  

On the equinoxes, the very center of the Sun sets exactly 12 hours after it rises. But the day actually begins when the upper edge of the Sun reaches the horizon (sunrise), and it doesn't end until the entire Sun has set.

In addition, there's a little known fact that the Sun is actually visible (briefly) when it is below the horizon.  The Earth's atmosphere refracts the Sun's rays and bends them in an arc over the horizon. For more on that click here to learn how our atmosphere bends light.

After all the pitfalls so far this 2020, I don't know about you, but I'm really looking forward to a new season

Discussing this and much more, be sure to join Lisa and I for our next installment  of #WxLIVE at 845 as we introduce the new season.  See you Tuesday evening!


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