What the 1st day of spring really means

File photo of a sun halo. March 20 is the first day of spring in the Northern Hemisphere. (Erik Sandoval, Copyright 2023 by WKMG ClickOrlando - All rights reserved.)

JACKSONVILLE, Fla. – It may not feel like it, but Monday is the first day of spring.

The exact time for the first day of spring is 5:24 p.m.

What exactly does the first day of spring really mean? And what is exactly is an equinox?

The astronomy of spring

Earth’s seasons are governed by astronomy.

The four seasons are separated by four major events — two equinoxes and two solstices.

The four seasons are based on the tilt of the Earth.

A solstice is when the sun’s direct rays reach their farthest northern or southern point. This is how summer and winter are governed.

Spring and fall are based on equinoxes. The spring equinox is officially known as the vernal equinox.

During the vernal equinox, the sun direct rays begin hitting the Earth just north of the Equator. This marks the start of the sun’s rays beginning their transit northward into the Northern Hemisphere.

Equal daylight?

The planet receives 12 hours of daylight and 12 hours of night during the spring equinox, but that doesn’t mean sunrise and sunset times are exactly 12 hours.

How can this be?

The sun is a disc, not a singular point of light.

The center of the sun will move above the horizon and leave the horizon in exactly 12 hours in an equinox, but we still get some of the rays before and after that point.

The sunrise time in Jacksonville on March 20 is 7:30 a.m., with the sunset at 7:37 p.m.

This is close to 12 hours but not exact: It’s 12 hours, 7 minutes of daylight.

Sunrise and sunset times were exactly 12 hours on March 16.

Jacksonville saw exactly 12 hours of daylight on March 16.

The city will see 12 hours of daylight again on Sept. 27 as we head toward the autumnal equinox.

What about the egg thing?

You may have heard that eggs will stand upright during the vernal and autumnal equinox.

File photo of eggs in a container. There is an urban legend that eggs can balanced upright during the vernal and autumnal equinoxes.

This is true.

But it is also true the other 364 days of the year.

Balancing an egg has nothing to do with the equinox. It is more a result of the curvature of an individual egg and the precise location of the yolk inside the egg.

Egg balancing is no different on the vernal equinox as it is on any other day.

Meteorological vs. astronomical spring

While spring “officially” starts on March 20, this is considered astronomical spring as the date is tied to the equinox.

Meteorologists use a different date to define season.

Meteorological spring started on March 1 and will last until May 31.

The difference between Astronomical and Meteorological Spring.

This difference is created by meteorologists and climatologists to define seasons — but by temperature.

The three coldest months in the Northern Hemisphere are December, January and February. The three warmest months are June, July and August.

Spring fits between the two stretches, with March, April and May the transition between the two.

Having full calendar months also helps create a more accurate sample size. Because of Earth’s elliptical orbit, a season can vary between 89 and 93 days.

Basing the seasons of full months creates more consistency.

Whether you observe meteorological or astronomical spring, mid-March is a clear indication that the move toward the summer season has begun.

About the Author:

David Heckard is The Weather Authority's Assistant Chief Meteorologist.