Equinox comes before the first day of spring for DC region

While meteorologists observe the first day of spring on March 1 for ease of weather-keeping records, the official first day of spring or “vernal equinox” arrives Monday. However, the balance of daylight and darkness is offset from the first day of spring.

Since we need a reason to celebrate, find joy in the fact that today we have 12 hours of daylight and darkness in the D.C. area. Yes, the sunrise and sunset are both 7:17 (a.m. and p.m.) on Friday.

Vernal equinox is a complicated way of saying “first day of spring,” but the “equinox” part refers to equal 12 hours of daylight and darkness.

Since the Earth is not a perfect circle, but rather an oblate spheroid, and light is bent as it comes through the atmosphere, Friday is the day when the region sees 12 hours of daylight and darkness.

On Saturday, we gain three more minutes of daylight, so the sunrise is two minutes earlier (7:15 a.m.) and sunset is one minute later at 7:18 p.m.

This year, Monday is the official day defined as the vernal equinox, which refers to the day and time (5:24 p.m. Eastern) when the sun moves overhead across the equator.

An image showing that seasons are caused by the fact that the Earth is tilted on its axis by 23.5 degrees (Courtesy NOAA).

Not everywhere in the U.S. has 12 hours of daylight and darkness Friday. Tucson, Arizona, and San Antonio, Texas, for instance, see 12 hours and two minutes of daylight today.

The 12-hour daylight/darkness benchmark also varies by a day or so. For instance, next year, Washington, D.C., will observe the “equinox” of daylight and darkness on March 16.

In an effort to avoid confusion when calculating seasonal averages, meteorologists use the standard March 1 to May 31 time frame for spring, June 1 to Aug. 31 for summer, Sept. 1 to Nov. 30 for autumn averages and Dec. 1 to Feb. 28 (or Feb. 29 for leap years) for winter averages.

Chad Merrill

Chad Merrill is a meteorologist and digital weather content producer for WTOP. Prior to joining WTOP, Chad was a meteorologist in the private industry and television. He loves to share his passion with listeners and readers and is eager to hear from anyone who has any weather questions!

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