Rim Country and White Mountain residents eager to feel the crisp autumn air now have official cause for celebration. The autumnal equinox will occur at 7:21 a.m. Arizona time on Monday, September 23rd. The date is worthy to note on the calendar because it signals the end of summer and the first day of fall in the northern hemisphere. (A translation of equinox means “equal night,” from the Latin words for aequus, equal and nox, night.) 

 

   Equinoxes occur twice per year when winter gives way to spring and when summer turns into fall. These are the two days of the year when day and night are of approximately equal duration everywhere on Earth. After the fall equinox, nights will continue to grow longer until the longest night of the year on the winter solstice in December.

   A common misconception is that seasonal changes occur because the Sun is closer to the Earth in the summer and farther away in the winter. Instead, seasonal changes are largely due to the 23 ½-degree tilt of the Earth’s axis relative to the plane of its orbit around the Sun. Therefore, when the north pole is tilted toward the Sun, our northern days are warmer and longer. When the south pole is angled toward the Sun, the southern hemisphere experiences summertime temperatures while we in the northern hemisphere are experiencing winter. The upper and lower extreme regions of the Earth experience the most dramatic changes due to seasonal variations. The polar bears in the Arctic (northern hemisphere) begin to put on pounds in preparation for winter hibernation while the penguins residing in the Antarctic (southern hemisphere) begin to molt, search for mates and bask in the warmer springtime temperatures.

   The fall equinox signals the onset of colder weather and shorter days for Rim Country and White Mountain residents. Clear, crisp nights and longer astronomical viewing times will provide great stargazing opportunities. 

   The official arrival of fall is a time to celebrate the procession of the seasons and the emergence of the celestial wonders of autumn skies.