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Posted at 09:51 AM ET, 03/19/2012

Spring equinox marks the official end of winter early Tuesday morning


Spring sunrise over the Jefferson Memorial as cherry blossoms hit peak bloom. (Kevin Ambrose)
Meteorologists consider March 1 the first day of spring, and this year it has certainly felt like it. Recent summerlike warmth across much of the country makes it hard to believe that winter has not officially ended – at least not according to the traditional definition of the seasons.

But the vernal equinox eliminates any doubt about which season we are in. On March 20 at 1:14 a.m. EDT, the sun’s rays shine directly overhead at the equator, which results in about 12 hours of daylight and darkness at all latitudes (see live satellite image of sunlight on Earth). This year’s equinox is the earliest since 1896.

The spring equinox marks the first day of spring in the Northern Hemisphere (and the first day of fall for our Southern Hemisphere neighbors). Until the summer solstice in June, the sun will continue its apparent northward migration toward the Tropic of Cancer, bringing us even more daylight while the sun angle increases by 23.5º at midday.


Table of sunrise, sunset, and day length in Washington, D.C. (Timeanddate.com, U.S. Naval Observatory, Gaisma.com, adapted by CWG)

On the spring equinox in Washington, D.C. the sun rises at 7:11 a.m. and set at 7:21 p.m. Together with the fall equinox in September, it is one of only two days of the year when the sun rises due east and sets due west of us. Over the next three months, we will see the sun rise and set increasingly to our northeast and northwest, respectively. In fact, this northward movement of sunrise and sunset is true for all locations north of the equator (except at very high latitudes near the North Pole).

Link: Share your spring photography

Although equinox means “equal night” in Latin, the sun is actually above the horizon for slightly more than 12 hours on the spring equinox. D.C. already saw its equal day and night on March 16 when sunrise and sunset were exactly 12 hours apart (7:17 a.m. and 7:17 p.m.). The exact date of a location’s equal day and night depends on latitude, but it usually occurs a few days before the spring equinox in the Northern Hemisphere.

Read more: Why the equinoxes do not have exactly 12 hours of daylight

Big gains in morning and evening light

If you live in the mid-latitudes of the Northern Hemisphere, you will notice the greatest increases in day length during the month of March (read why here). Washington, D.C. gains as much as 2 minutes and 33 seconds of daylight each day at this time of year. We started the month of March with the sun above the horizon for 11 hours and 21 minutes, but by March 31 the sun will shine for 12 hours and 37 minutes.


Comparison of day length for select U.S. cities during the month of March. Cities at higher latitudes experience greater increases in daylight at this time of year. (timeanddate.com, adapted by CWG)
How much daylight is gained depends on one’s latitude. The farther north you go, the greater the increase. In fact, between the spring and fall equinox, cities north of us will actually receive more daylight than cities to our south.

No matter what your location in the Northern Hemisphere, however, daylight will exceed nighttime darkness for the next six months.

Additional Reading:

Detailed sunrise/set table for Washington, D.C.
Sunrise/sunset calculator for cities around the world
The March equinox explained
Equal day and night - but not quite
Earth satellite images of the solstices and equinoxes (NASA Earth Observatory)
How the location of sunrise and sunset changes throughout the year

More from Capital Weather Gang

The summer solstice and other sun facts explained
Longer nights and shorter days: the autumnal equinox explained
The winter solstice and other sun facts explained

By  |  09:51 AM ET, 03/19/2012

Categories:  Astronomy, Latest

 
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