A brief, scientific guide to the first day of spring.
This article, by Brian Resnick, appeared on VOX on March 18, 2019. We have excerpted sections of the article that we thought you might enjoy...
The vernal equinox is upon us: On Wednesday, March 20, both the Northern and Southern hemispheres will experience an equal amount of daylight. For those of us in the Northern Hemisphere, it marks the beginning of spring, with daylight hours continuing to lengthen until the summer solstice in June. For those south of the equator, it’s the beginning of autumn.
Technically speaking, the equinox occurs when the sun is directly in line with the equator. This will happen at 5:58 pm Eastern time on Wednesday.
The equinox, the seasons, and the changing length of daylight hours throughout the year are all due to one fact: The Earth spins on a tilted axis.
The tilt — possibly caused by a massive object hitting Earth billions of years ago — means that for half the year, the North Pole is pointed toward the sun. For the other half of the year, the South Pole gets more light. It’s what gives us seasons.
Equinox literally means “equal night.” And during the equinox, most places on Earth will see approximately 12 hours of daylight and 12 hours of night.
But not every place will experience the exact same amount of daylight. For instance, on Wednesday, Fairbanks, Alaska, will see 12 hours and 15 minutes of daylight. Key West, Florida, will see 12 hours and six minutes. The differences are due to how the sunlight gets refracted (bent) as it enters Earth’s atmosphere at different latitudes.
That daylight is longer than 12 hours on the equinox is also due to how we commonly measure the length of a day: from the first hint of the sun peeking over the horizon in the morning to the very last glimpse of it before it falls below the horizon in the evening. Because the sun takes some time to rise and set, it adds some extra daylight minutes.
Check out TimeAndDate.com to see how many hours of sunlight you’ll get during the equinox.