Vernal Equinox: Science Behind the First Day of Spring 2017

March 20, 2017

The vernal equinox, officially bringing the arrival of spring, happens Monday morning.

During the equinox, nearly equal amounts of daylight and darkness are experienced throughout the world.

Twice a year, around March 20 or 21 and September 22 or 23, the sun's most direct rays shine on the equator. These two days are known as the vernal (spring) equinox and the autumnal (fall) equinox, respectively.

This year, the vernal equinox takes place on Monday, March 20 at 6:29 a.m. EDT. At this time, the sun's most direct rays cross over from the southern hemisphere into the northern hemisphere. During this process, the sun is shining directly over the earth's equator, bathing the earth's northern and southern hemispheres in nearly an equal amount of sunlight.

(MORE: How Weather Impacts Your Spring Allergies)

Instead of a tilt away from or toward the sun, the Earth's axis of rotation is perpendicular to the line connecting the centers of the Earth and the sun during an equinox. During the equinox, both day and night are balanced to nearly 12 hours each all over the world.

Good news for those in the northern hemisphere: Daylight continues to grow longer until the summer solstice, which occurs on Wednesday, June 21. The opposite occurs in the southern hemisphere, where daylight continues to grow shorter toward their winter solstice on the same day.

MORE: Scenes from the First Day of Spring


The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

Ad Blocker Enabled

Featured Blogs

Meteorology of Saturday's Colombian Flood Disaster That Killed 254

By Dr. Jeff Masters
April 3, 2017

At least 254 people were killed in the in the city of Mocoa (population 40,000) in southwest Colombia near the border of Ecuador early Saturday, when torrential rains triggered a debris flow on a nearby mountain that surged into the town as a huge wall of water carrying tons of mud and debris. The disaster is the fourth deadliest weather-related disaster in Colombia’s recorded history.

Iconic American Destination Virtually Isolated for Rest of Year

By Christopher C. Burt
March 24, 2017

Half of the village of Big Sur, on the coast of central California, has lost its only access to the north following the demolition of the flood-damaged Pfeiffer Canyon Bridge along State Route 1 (also Rt. 1 or SR 1) on March 19. Although Rt. 1 to the south of Big Sur has reopened to traffic (after mud and rock slides were cleared) it is a long 70-mile journey along the windy but spectacular highway to Cambria, the next town of any significance where supplies can be had. CalTrans (California Department of Transportation) estimates it will take 6-9 months to rebuild a new bridge over the canyon.

An extraordinary meteorological event; was one of its results a 1000-year flood?

By Stu Ostro
October 5, 2015

The confluence of meteorological ingredients the first weekend in October 2015 resulted in an extraordinary weather event with severe impacts. Was one of them a 1000-year flood?

Why the Arrest of a Science-Loving 14-year-old Matters

By Shaun Tanner
September 16, 2015

By now, many of you have heard or read about the arrest of Ahmed Mohamed, a 14-year-old high school student from Irving, Texas. Ahmed was arrested because school officials called the police after he showed one of his teachers his homemade clock. Mistaken for a bomb, Ahmed was taken into custody, interrogated, shamed, suspended (still on suspension today, Wednesday), and reprimanded. All of this after it has been found that the "device" he brought to school was indeed, a homemade clock.