Even though it’s still cold outside, Monday’s equinox serves as a reminder that warmer days are just around the corner. The end of winter and the start of spring are marked in the Northern Hemisphere by the vernal (or spring) equinox, which occurs March 20 at 5:24 p.m. Eastern time.
Twice a year, in March and September, there are equinoxes. They commemorate the precise moment in time when the sun appears straight over the equator of the Earth and takes place halfway between the winter and summer solstices.
Direct sunlight from the sun enters the Northern Hemisphere during the March equinox. In North America, Europe, and Asia, it is the first day of astronomical spring; in the Southern Hemisphere, summer is turning into fall.
We don’t orbit the sun exactly vertically, which is why we have equinoxes and seasons. The Northern and Southern hemispheres receive varying quantities of sunshine throughout the year due to Earth’s tilt on its axis, which is around 23.5 degrees. Nonetheless, the sun’s energy is distributed equally between the two hemispheres on the spring and fall equinoxes. Day and night are therefore virtually equal everywhere on Earth.
Equal day and night? Not quite
Although the word “equinox” is derived from the Latin words “aequus” (meaning “equal”) and “nox” (meaning “night”), day and night do not last exactly 12 hours.
For instance, on a Monday, Washington, D.C. Experience 12 hours and 8 minutes of daylight, with dawn at 7:11 a.m. and sunset at 7:19 p.m. For the majority of the Lower 48 States, the “equinox,” or day when sunrise and sunset come closest to being 12 hours apart, takes place on March 16 or 17.
There are two explanations for why the equinox has more than 12 hours of daylight.
One is how we determine what a “sunrise” and “sunset” mean regarding how long a day is. Instead of being a distinct point in the sky like a star at night, the sun appears as a disc. Sunset doesn’t happen until the sun’s upper edge completely descends below the horizon; sunrise happens as soon as it does. It usually takes a few minutes for the sun to completely depart from the sky if you’ve ever observed a sunset.
The sun’s light can also be bent or refracted by the Earth’s atmosphere. We can see the sun at sunrise and sunset even though it is technically below the horizon because of this optical illusion.
Combined, air refraction and how we determine how long a day is given the equinox several extra minutes of daylight. The length of daylight in Earth’s polar regions is roughly 12 hours 20 minutes, compared to 12 hours 6 minutes at the equator.
The places where dawn and sunset occur shift
The only times of the year when the sun rises in the east and sets in the west, regardless of where you reside, are on the spring and fall equinoxes. Only near the North and South poles, where the sun is either rising or setting for the first time in six months, does this not apply.
As the sun travels a longer and higher course through the sky, the position of sunrise and sunset will continue to move closer to the northern horizon from now until the summer solstice. The sun moves further south after the summer solstice, and the days grow shorter once more.
Springtime temperature forecast
As we go closer to summer, the number of daylight hours will definitely increase along with the temperature. Recently, the National Oceanic and Atmospheric Administration published its spring 2023 outlook, which predicts above-average temperatures over the eastern and south-central United States. The temperatures in spring may come near to the long-term average across the northern Plains, the West Coast, and the Rockies.