Robert B. Decker: Autumnal Equinox

In 2020, the autumnal equinox—also called the September equinox or fall equinox—arrives on Tuesday, September 22nd. Fall begins in the Northern Hemisphere and is a reminder that summer is now officially behind us.

The equinox, which happens around Sept. 22 or 23 every year, is a rather fleeting astronomical event. It happens at a precise moment when the sun's direct rays are straight over Earth's equator. This year's equinox is at 9:30 a.m. Eastern time on September 22nd. Based on the astronomical definition of seasons, the autumnal equinox marks the first day of fall (in the Northern Hemisphere). However, according to the meteorological definition of seasons, which is based on temperature cycles and the Gregorian calendar, the first day of fall is September 1st.

The word is derived from the Latin words aequus (equal) and nox (night). On the day of an equinox, daytime and nighttime are of approximately equal duration all over the planet. But the exact amount of daylight depends on your distance from the equator. At higher latitudes, such as northern Alaska, the sun is up for more than 12 hours and 20 minutes on the equinoxes.

The autumnal equinox is roughly the halfway point between our longest and shortest days of the year. Over the next three months, you'll notice the sun rising and setting closer to the southern horizon. And the sun will trace a shorter and lower path across the sky. This will end with the December or Winter solstice, when days start to grow longer and nights shorter.

The fall season also brings an opportunity for celebration! Many festivals are associated with autumn around the world, like the Alba White Truffle Festival in Italy, Diwali in India, Bonfire Night in the UK, Thanksgiving in United States, and Halloween, which is celebrated all over the world!

Here are some of my favorite national parks that I've visited in the fall...

Click here to see the Blue Ridge Parkway poster.