March Equinox: March 20, 2013, 11:02 UTC

There are two equinoxes every year – in March and September – when the sun shines directly on the equator and the length of day and night is nearly equal. Seasons are opposite on either side of the equator, so the equinox in March is also known as the "spring equinox" in the northern hemisphere. However, in the southern hemisphere, it's known as the "autumnal (fall) equinox".

The Earth's position during the equinox (ill. not to scale).

March Equinox in Palo Alto, California, U.S.A. was on
Wednesday, March 20, 2013 at 4:02 AM PDT (Change city)

March Equinox in Universal Coordinated Time was on
Wednesday, March 20, 2013 at 11:02 UTC

• Local times for March Equinox 2013 worldwide
• Sunrise, sunset and daylength around March Equinox 2013
• Day and Night map for March Equinox 2013
• Equinoxes and solstices from 2000–2049

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, even if this is widely accepted, it isn't entirely true. In reality equinoxes don't have exactly 12 hours of daylight

The March equinox occurs 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 either on March 19, 20 or 21 every year. 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 Earth's axis tilts neither away from nor towards the Sun, like the illustration shows.

                                           June Solstice | December solstice | September equinox

Spring Equinox at Chichen Itza, Mexico, with the sunlight forming the snake on the staircase.

©iStockphoto.com/CostinT

Celebrating new beginnings

In the northern hemisphere the March equinox marks the start of spring and has long been celebrated as a time of rebirth. Many cultures and religions celebrate or observe holidays and festivals around the March equinox, like the Easter and Passover.

Holidays around the September equinox.

Cultural importance

Equinoxes – along with solstices – have been celebrated in cultures all over the world for as long as we have written history. One of the most famous ancient Spring equinox celebrations was the Mayan sacrificial ritual by the main pyramid in Chichen Itza, Mexico.

The snake of sunlight

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 at the precise moment of the equinox.

iPhone & iPad app:
Day and Night World Map
Watch the sun move across the sky.

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

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 .