Humanities › Geography When Is the Spring Equinox? Does the Spring Equinox Begin on March 19 or 20? Share Flipboard Email Print Westend61 / Getty Images Geography Physical Geography Basics Political Geography Population Country Information Key Figures & Milestones Maps Urban Geography By Matt Rosenberg Geography Expert M.A., Geography, California State University - Northridge B.A., Geography, University of California - Davis Matt Rosenberg is an award-winning geographer and the author of "The Handy Geography Answer Book" and "The Geography Bee Complete Preparation Handbook." our editorial process Matt Rosenberg Updated March 16, 2019 Depending on where you live in the Northern Hemisphere, the vernal equinox (better known as the first day of spring) begins every year on March 19 or 20. But what exactly is an equinox, and who decided that was when spring should begin? The answer to those questions is a little more complicated than you may think. The Earth and the Sun To understand what an equinox is, you must first know a little bit about our solar system. The earth rotates on its axis, which is tilted at 23.5 degrees. It takes 24 hours to complete one rotation. As the earth spins on its axis, it also orbits around the sun, which takes 365 days to complete. During the year, the planet slowly tilts on its axis as it orbits the sun. For half the year, the Northern Hemisphere—the portion of the planet that lies above the Equator—receives more sunlight than the Southern Hemisphere. For the other half, the Southern Hemisphere receives more sunlight. But on two days each calendar year, both hemispheres receive an equal amount of sunlight. These two days are called equinoxes, a Latin word that means "equal nights." In the Northern Hemisphere, the vernal (Latin for "spring") equinox occurs on March 19 or 20, depending on which time zone you live in. The autumnal equinox, which signals the start of fall, begins on September 21 or 22, again depending on which time zone you're in. In the Southern Hemisphere, these seasonal equinoxes are inverted. On these days, day and night both last 12 hours, although the daylight can actually last up to eight minutes longer than night due to atmospheric refraction. This phenomenon causes sunlight to bend around the curve of the earth, depending on conditions such as atmospheric pressure and humidity, allowing light to linger after sunset and appear before sunrise. The Start of Spring There's no international law that says spring must begin on the vernal equinox. Humans have been observing and celebrating seasonal changes based on how long or short the day is since time began. That tradition became codified in the Western world with the advent of the Gregorian calendar, which linked the change of seasons to the equinoxes and solstices. If you live in North America, the vernal equinox in 2018 begins at 6:15 a.m. in Honolulu, Hawaii; at 10:15 a.m. in Mexico City; and at 1:45 p.m. at St. John's, Newfoundland, Canada. But because the earth doesn't complete its orbit in a perfect 365 days, the start of the vernal equinox changes annually. In 2018, for example, the equinox begins in New York City at 12:15 p.m., Eastern Daylight Time. In 2019, it doesn't begin until 5:58 p.m. on March 20. But in 2020, the equinox starts the night before, at 11:49 p.m. At the other extreme, the sun at the North Pole lies on the horizon of the earth's surface on the March Equinox. The sun rises at noon to the horizon on the March Equinox and the North Pole remains lit until the autumnal equinox. At the South Pole, the sun sets at noon after endless daylight for the previous six months (since the autumnal equinox). The Winter and Summer Solstice Unlike the two equinoxes when days and nights are equal, the two annual solstices mark the days when the hemispheres receive the most and least sunlight. They also signal the beginning of summer and winter. In the Northern Hemisphere, the summer solstice occurs on June 20 or 21, depending on the year and where you live. This is the longest day of the year north of the equator. The winter solstice, the shortest day of the year in the Northern Hemisphere, occurs on December 21 or 22. It's the opposite in the Southern Hemisphere. Winter begins in June, summer in December. If you live in New York City, for example, the 2018 summer solstice occurs at 6:07 a.m. on June 21 and the winter solstice at 5:22 p.m. on Dec. 21. In 2019, the summer solstice starts at 11:54 a.m., but in 2020, it occurs at 5:43 p.m. on June 20. In 2018, New Yorkers will mark the winter solstice at 5:22 p.m. on Dec. 21, 11;19 p.m. on the 21st in 2019, and 5:02 a.m. on the 21st in 2020. Equinoxes and Eggs It is a widely held assumption that one can only balance an egg on its end on the equinoxes but this is simply an urban legend that began in the U.S. after a 1945 Life magazine article on a Chinese egg-balancing stunt. If you're patient and careful, you can balance an egg on its bottom anytime. Sources Byrd, Deborah. "March Equinox! Happy Spring or Fall." EarthSky.org. 20 March 2017.Epstein, Dave. "Why is Monday Considered Spring? The Vernal Equinox, Explained." BostonGlobe.com 20 March 2017.History.com staff. "Vernal (Spring) Equinox." History.com.Royal Museums Greenwich staff. "Equinoxes and Solstices." RMG.org.