When is the first day of spring? You’ve heard of equinox. It happens every year. Twice, actually. But do you understand it? Could you explain it to a child?
Here’s everything you need to know about the vernal or spring equinox in 2023—when it is, what it is and why this year it’s a great time to go stargazing.
When is the spring equinox?
This year the spring equinox—the beginning of astronomical spring in the northern hemisphere—will occur on Monday, March 20 at 21:25 UTC. That translates as these times in North America:
5:25 p.m. EDT
4:25 p.m. CDT
3:25 p.m. MDT
2:25 p.m. PDT
1:25 p.m. AKDT
12:25 p.m. HDT
What is the spring equinox?
It’s one of four markers of Earth’s annual orbit around the Sun. Like the other equinox in late September it marks a moment when the Sun is above the equator, bringing equal night and equal day to both hemispheres (equinox is Latin: equi (equal) and nox (night).
The spring equinox is when the Sun crosses the celestial equator going north, marking the transition from winter to spring in the northern hemisphere and summer to fall in the southern hemisphere.
The other two markers are the solstices in late June and late December, which mark the days with the longest period of daylight and longest period of darkness, respectively.
Why do equinoxes occur?
Equinoxes and solstices mark the start and end of seasons. Seasons are the direct result of our planet’s tilted axis, which changes the amount and intensity of sunlight bestowed on each hemisphere. Summer in the northern hemisphere—marked by June’s solstice—is when that half of the planet is tilted towards the Sun. The days are longer and more sunlight reaches it. Winter is the opposite.
Equinoxes are when the planet is side-on to the Sun—when the tilt of the Earth’s axis is not tilted towards or away from the Sun, which sends equal amounts of daylight and darkness to all parts of our planet.
Why is this equinox a great time to go stargazing?
The very next day after the spring equinox, at 17:23 UTC, a New Moon occurs. Since a New Moon is roughly between the Earth and the Sun it is utterly invisible and its light never features it the night sky. It thus makes the night as dark as possible. It makes a massive difference if you’re trying to find faint star clusters and constellations.
As the weeks draw on after equinox the days get longer than the nights—culminating in solstice, the longest day of the year—making stargazing ever more difficult, particularly for those in northern latitudes, where is never truly gets dark in June. However, equinox itself is this year an excellent time to go stargazing because the night skies will be as dark as they ever get.
How to see the equinox
The Sun being directly over the equator isn’t much to see, is it? The best way to “see” an equinox or a solstice is to watch at sunrise or sunset. Only an equinox does the Sun rises due east and sets due west, which over the centuries has meant something to many ancient cultures.
As well as simply watching the Sun rise and set with the cardinal points, you could also travel to an ancient place to see the various alignments. Those places include, but are not limited to:
Stonehenge and Avebury, England
Chichen Itza, Mexico
Machu Picchu, Peru
Temple of Karnak, Egypt
During Earth’s annual orbit around the Sun, different parts of the planet get different amounts of sunlight—except at the equinoxes. Humans have known about this for thousands of years and celebrated the changing of the seasons. How will you mark the equal day, equal night?