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March equinox - equal day and night, nearly

There are two equinoxes every year – in March and September – when the Sun shines directly on the equator and the length of night and day are nearly equal, but not quite.

Illustration image
The Earth during the equinox. (Not to scale)
On the equinox the Earth's axis tilts neither away from nor towards the Sun and is perpendicular to the Sun's rays. (Not to scale)

The Sun crosses equator

The March equinox marks the moment the Sun crosses the celestial equator – the imaginary line in the sky above the Earth’s equator – from south to north. This happens on March 19, 20 or 21 every year.

When is the equinox in my city?

Why is it called “equinox”?

On the equinox, night and day are nearly exactly the same length – 12 hours – all over the world. This is the reason it's called an “equinox”, derived from Latin, meaning "equal night". However, in reality equinoxes don't have exactly 12 hours of daylight

Spring in the north, fall in the south

Equinoxes and solstices are opposite on either side of the equator, and the March equinox is also known as the "spring (vernal) equinox" in the northern hemisphere and as the "autumnal (fall) equinox" in the southern hemisphere.

March Equinox in Washington DC, District of Columbia, U.S.A. was on
Thursday, March 20, 2014 at 12:57 PM EDT (Change city)

March Equinox in Universal Coordinated Time was on
Thursday, March 20, 2014 at 16:57 UTC

What happens on the equinox?

The Earth's axis is always tilted at an angle of about 23.5° in relation to the ecliptic, the imaginary plane created by the Earth's path around the Sun. On any other day of the year, the Earth's axis tilts a little away from or towards the Sun. But on the two equinoxes, the tilt of the Earth's is neither away from nor towards the Sun. In fact, it is perpendicular to the Sun's rays, like the illustration shows.

Celebrating new beginnings

The March equinox has long been celebrated as a time of rebirth in the Northern Hemisphere. Many cultures celebrate spring festivals and holidays around the March equinox, like Easter and Passover.

The snake of sunlight

One of the most famous ancient Spring equinox celebrations was the Mayan sacrificial ritual by the main pyramid at Chichen Itza, Mexico.

The main pyramid – also known as El Castillo – has four staircases running from the top to the bottom of the pyramid's faces, notorious for the bloody human sacrifices that used to take place here.

The staircases are built at a carefully calculated angle which makes it look like an enormous snake of sunlight slithers down the stairs on the day of the equinox.

Illustration image

“The snake of sunlight” on the stairs of the main pyramid at Chichen Itza, Mexico.

©iStockphoto.com/CostinT

The Mayan calendar was very precise in this respect, but today the Mayan calendar is most famous for ending exactly at 11:11 UTC on the 2012 December Solstice .

Knowledge of the equinoxes and solstices is also crucial in developing dependable calendars, another thing the Mayans clearly had got the hang of.

Topics: Astronomy, Sun, Earth, Seasons, March

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Equinox & Solstice

  1. March Exquinox
  2. June Solstice
  3. September Equinox
  4. December solstice

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When is fall equinox?

The fall (autumnal) equinox in the Northern Hemisphere is in September. In the Southern Hemisphere it's in March. more