For the next six months, we’ll be seeing a lot more daylight than darkness.
By Justin GrieserMarch 19, 2021 at 12:00 p.m. MDTAdd to list
Signs of spring are everywhere: Birds are chirping, daffodils are emerging and blooming trees mean it’s time to start fretting about allergies. On Saturday, the new season becomes official: March 20 is the vernal equinox, marking the first day of spring in the Northern Hemisphere.
Although the weather may still feel chilly, we are experiencing just over 12 hours of daylight and the sun appears noticeably higher in the sky. With winter behind us, we’re now entering the warmer, sunnier and brighter half of the year.
What happens on the equinox?
Equinoxes occur twice a year — once in March and once in September at a precise moment in time.
On the March equinox, which arrives Saturday at 5:37 a.m. Eastern time, the sun’s direct rays appear straight over the equator before shifting into the Northern Hemisphere. We’re halfway between the winter and summer solstice, which means neither daylight nor darkness has the upper hand. In the Southern Hemisphere, summer has ended and autumn is beginning.
The reason we have equinoxes is because we don’t orbit the sun completely upright. The Earth is tilted on its axis by about 23.5 degrees, causing one hemisphere to receive more of the sun’s light and energy at different times of year.ADhttps://1aa6b244146b688ebcf01fdf2fbf3aa6.safeframe.googlesyndication.com/safeframe/1-0-37/html/container.html
On the equinox, however, the sun’s rays directly strike the equator — the dividing line between Earth’s two hemispheres — which means day and night are nearly equal everywhere on Earth.
The exact time and date of the March equinox changes slightly each year. In most years, it falls on the 20th. In 2020, however, the equinox arrived March 19 in North America — as it will on every leap year for the rest of this century.
To avoid confusion between time zones, the official time of the equinox is based on Coordinated Universal Time (UTC), which is four hours ahead of Eastern Daylight Time. By this metric, a March 21 equinox hasn’t occurred since 2007, and won’t happen again until the year 2102, according to timeanddate.com.
Day and night not perfectly equal
Though “equinox” comes from the Latin words “aequus” (equal) and “nox” (night), both of Earth’s hemispheres actually see slightly more than 12 hours of daylight on the equinox.
In Washington, we’ll see 12 hours 9 minutes of daylight on Saturday, with sunrise at 7:11 a.m. and sunset at 7:20 p.m.
The imbalance happens for two reasons, one being how we measure the length of a day. The sun appears as a lumbering disc, and not a discrete point in the sky. Sunrise occurs as soon as the sun’s upper edge appears on the horizon, while sunset doesn’t happen until the sun’s upper edge completely dips below it.
Moreover, the Earth’s atmosphere can refract, or bend, the sun’s light, allowing us to see the sun even when it’s technically below the horizon. Daylight on the equinox therefore varies — from 12 hours 6 minutes near the equator to about 12 hours 20 minutes in Earth’s polar regions.
Increasing daylight and shifting sunrise and sunset
The equinoxes are the only two days of the year when the sun rises perfectly due east and sets due west along the horizon — regardless of your location. (The only place this doesn’t apply is at the North and South poles, where the sun is either rising or setting for the first time in six months.)
For the next three months, you’ll notice the sun rise and set a bit farther to the north as it takes a longer and steeper path through the sky.
Though the days have steadily been getting longer since the winter solstice, the increasing day length is especially noticeable around the spring equinox; it’s when we gain daylight at our fastest clip of the year.
In the nation’s capital, the amount of daylight increases from 11 hours 21 minutes on March 1 to 12 hours 40 minutes on April 1. Around the equinox, we’re gaining 2 minutes 32 seconds of daylight each day.
The increase is greater in locations to our north, but less pronounced as you head closer to the equator. Boston, for example, tacks on 2 minutes 52 seconds per day, while in Miami the daily increase is only about 90 seconds.
As the days lengthen and the sun climbs higher in the sky, temperatures will continue their inevitable ascent toward summer. D.C.’s average high temperature, now 57 degrees, hits 60 on March 27 and climbs to 71 degrees by late April.
This year, it looks like winter won’t hang on too much longer. In its spring 2021 outlook released this week, the National Oceanic and Atmospheric Administration is forecasting warmer-than-average temperatures across most of the United States.
While spring always has its share of wild temperature swings, the equinox is a reminder that warmer days are just around the corner.