Spring officially begins today (March 20) with the vernal equinox, bringing longer days and warmer temperatures to the Northern Hemisphere.
The vernal equinox signals the astronomical start of spring in the Northern Hemisphere, with the sun crossing above Earth’s equator, moving from south to north, at 5:01 a.m. EST (0901 GMT) on March 20. This means that after months of being pointed away from the sun during the winter, the Northern Hemisphere will now begin pointing toward the sun, according to In-the-Sky.org.
As the Northern Hemisphere welcomes spring today, the Southern Hemisphere greets the first day of autumn.
The word equinox is derived from the Latin words “aequus” (equal) and “nox” (night). There are two equinoxes in the year — vernal in the spring and autumnal in the fall — when daylight and night are roughly equal due to the Earth’s tilt and the planet’s position in its orbit around the sun.
Earth experiences seasonal changes because its axis is tilted so different areas of the planet face the sun’s direct rays through the year. When the North Pole tilts toward the sun, it’s summer in the Northern Hemisphere, where the sun’s rays shine directly north of the equator. However, when the South Pole tilts toward the sun, it’s winter in the Northern Hemisphere, as sunlight beams down directly over areas south of the equator.
“On the day of the equinox, everywhere on Earth has almost exactly 12 hours of day and night, as the sun’s annual journey through the constellations of the zodiac carries it across the celestial equator,” according to the statement from In-the-Sky.org. “Wherever you live on Earth, on the day of the equinox the sun will rise from the point on the horizon which lies due east, and set beneath the point which lies due west.”
While cold temperatures may still linger, daylight has already started to lengthen — especially for those in areas that observe daylight savings, which occurred on March 9, when clocks shifted one hour ahead. Now, the vernal equinox marks the tipping point into increasingly longer days until the summer solstice on June 20, the longest day of the year.
During the equinox in March and September — the intermediate points between the summer and winter solstices — the sun lies directly over Earth’s equator. As a result, spring and fall seasons feel similar in the Northern and Southern hemispheres, compared to the extremes of winter and summer. This also results in quicker sunsets during equinox, as the sun sinks speedily below the horizon over the next couple of days.
