When’s the First Day of Spring?

When Does Spring Begin? A Guide to the Spring Equinox

As the days slowly lengthen and a hint of warmth returns to the air, many of us eagerly anticipate the arrival of spring. But when exactly does spring begin? The answer is a bit more nuanced than you might think! While meteorological spring has its own start date, the official beginning of astronomical spring is marked by the spring equinox.

Understanding the Spring Equinox

The spring equinox, a pivotal moment in our yearly cycle, signifies the point when the sun crosses the celestial equator, resulting in roughly equal hours of daylight and darkness. In the Northern Hemisphere, this event consistently occurs between March 19th and 21st. This year, 2024, the spring equinox will arrive on March 19th at 11:06 PM EDT.

This date isn’t arbitrary. It’s determined by the Earth’s 23.5-degree axial tilt as it orbits the sun. This tilt causes different parts of the planet to receive varying amounts of sunlight throughout the year. The equinox happens twice annually – once in March (spring) and once in September (autumn). Importantly, the equinox occurs at the same instant globally. However, for those south of the equator, the spring equinox marks the beginning of autumn.

Equinox vs. Equilux: What’s the Difference?

You might hear the term ‘equilux’ thrown around. While often confused with the equinox, they aren’t the same. The equinox is defined by the sun’s position relative to the Earth. The equilux, however, is the day when we actually experience 12 hours of daylight and 12 hours of darkness.

Interestingly, in the UK (and many other locations), the equilux occurs before the equinox. This is due to atmospheric refraction – the bending of sunlight as it enters the Earth’s atmosphere. This effect makes the sun appear to rise slightly earlier and set slightly later, adding extra daylight hours. In 2024, the equilux occurred on March 18th in the UK.

Astronomical vs. Meteorological Spring

It’s also important to note the distinction between astronomical and meteorological spring. Meteorological spring, for weather forecasting purposes, always begins on March 1st. This allows for consistent year-to-year comparisons of weather data. Astronomical spring, as we’ve discussed, is tied to the Earth’s orbit and the equinox, and its date varies slightly each year.

Spring in the US and Beyond

While the equinox marks the astronomical start of spring for the entire Northern Hemisphere, the experience of spring varies greatly depending on location. The National Weather Service provides detailed seasonal outlooks for the US, including temperature and precipitation forecasts. Currently, the Southwestern US is experiencing record heat, even as spring begins. You can also find information about upcoming celestial events to watch for in the spring night sky. Space.com has a great guide.