The first day of spring, the vernal equinox, arrives today, March 20th, at 10:46 a.m. EDT (7:46 a.m. PDT). This marks the moment the sun shines directly over the equator, theoretically bathing both hemispheres in equal light. In reality, the sun will be positioned directly over the Atlantic Ocean, roughly 790 miles east of Macapá, Brazil.
The Shifting Date of Spring’s Arrival
Many remember the first day of spring as falling on March 21st. However, for North America, the equinox now consistently occurs on March 20th. This isn’t a recent change; during the 20th century, March 21st was actually the exception. From 1980 to 2102, the equinox will occur no later than March 20th, and by 2028, it will officially begin on March 19th in the Western Hemisphere.
This shift happens because Earth’s orbit isn’t a perfect circle, and our Gregorian calendar isn’t synchronized with it. The inclusion of leap days (particularly in years divisible by 400) further influences these seasonal date shifts. Without the leap year in 2000, today’s equinox would have fallen on March 21st instead. This highlights that our perception of seasons is tied to a human-made calendar that imperfectly reflects natural cycles.
Beyond the Myth of Equal Day and Night
The notion of equal day and night on the equinox is a common misconception. In fact, daylight is longer than darkness by several minutes on both the March and September equinoxes. This isn’t a matter of imprecise measurement; the difference is inherent in how we define sunrise and sunset.
The standard definition uses the top edge of the sun appearing over the horizon, not its center. But the bigger factor is atmospheric refraction: our atmosphere bends sunlight, making the sun appear higher than it actually is. Calculations by the U.S. Naval Observatory account for this effect, estimating that our atmosphere effectively extends daylight by approximately six to seven minutes.
This means that when you watch the sun rise or set, you’re seeing an illusion —the sun is technically still below the horizon. The atmosphere’s bending of light tricks us into perceiving longer days, even on the equinox itself.
In conclusion, the first day of spring is a fascinating intersection of astronomy, calendar mechanics, and atmospheric optics. While the equinox should represent equal day and night, the reality is more complex and visually deceptive. The sun’s apparent position and the bending of light ensure that days outpace nights from the very beginning of spring.
