Spring officially begins with the vernal equinox today – though it hardly feels like it in the eastern U.S., where winter is making an unwelcome comeback.
At 6:45 p.m. EDT on March 20, the sun appears directly overhead at Earth’s equator, marking the start of spring in the Northern Hemisphere. This year, the spring equinox has the unusual distinction of coinciding with both a supermoon and a total solar eclipse. According to timeanddate.com, there hasn’t been a solar eclipse on either the March or September equinox since 1662!
We won’t have to wait 353 years for the next equinox solar eclipse, however. Another total solar eclipse will occur on March 20, 2034, followed by an annular eclipse in 2053. Unfortunately, like this year’s eclipse, neither of these will be visible from North America.
But while much of the world missed out on today’s eclipse, there are still plenty of reasons to look skyward. The spring equinox is one of only two days of the year when all places on Earth (outside the polar regions) see the sun rise due east and set due west along the horizon. With neither hemisphere tilted away from or toward the sun, all latitudes get approximately 12 hours of daylight and darkness, as shown in the day and night world map below:
Although the word “equinox” means “equal night” in Latin, the sun is actually up for more than 12 hours in both hemispheres. Note how in Washington, D.C., the sun is already up for 12 hours and 8 minutes on the equinox, whereas sunrise and sunset were exactly 12 hours apart three days ago, on March 17:
What’s behind this? Blame atmospheric refraction. This optical phenomenon bends the sun’s light as it passes through Earth’s atmosphere and causes the sun to appear slightly higher on the horizon than it is in reality.
Another factor is how we define sunrise and sunset. Sunrise is defined as the moment the sun’s upper edge appears on the horizon, while sunset occurs when the upper edge disappears from the horizon.
Together, these factors add a few extra minutes of daylight to the equinox. In the Northern Hemisphere, the exact 12-hour day occurs a few days before the spring equinox, typically March 14-18, depending on one’s latitude.
Rapidly increasing daylight
The spring equinox marks the halfway point between the dark days of winter and the long, bright days of summer. While daylight has been increasing again since the winter solstice, the Northern Hemisphere sees its most dramatic gains in daylight a few weeks before and after the equinox. The greater one’s distance from the equator, the faster the change. During the month of March, D.C. gains one hour and 19 minutes of daylight, or about two minutes and 33 seconds each day.
For the next six months, any location to our north will see the sun above the horizon longer than we do. But after another brutal winter in the Northeast and Midwest this year, our northern neighbors certainly deserve those extra daylight hours. With below-average temperatures forecast in the eastern U.S. through the end of March, some places may have to wait a few more weeks for spring to finally show its face.