The 'official' start to spring? Here's how the equinox works

Sunday, March 19, 2017, 6:00 AM - The "official" start to spring is at 6:28 a.m. Monday, a welcome marker on the road to true warmth.

This year's winter has had its share of warm-ups and winter storms, and the March equinox is culturally tied to the changing of the season, but that date -- March 20 this year -- rarely has anything to do with how the seasons usually run in a given country.

Rather than being a product of the weather, the equinox is only, and exclusively, tied with the position of the Earth in its orbit around the sun. 

In a nutshell, the equinox occurs when the Earth's equator is aligned more or less exactly toward the sun, rather than one hemisphere being favoured over the other.

Image: Przemyslaw Idzkiewicz/Wikimedia Commons

On the dates of the equinox, day and night will be more or less of equal length -- hence the word "equinox," derived from a Latin term meaning "equal night."

After the March equinox (the "vernal" equinox in the north, the "autumnal" equinox in the south), the northern hemisphere will begin to receive more sunlight than the southern hemisphere, peaking on the July solstice, the longest day in the north and shortest day in the south.

For many cultures, the northern equinox isn't just the start of spring, it's also a reference for the start of their own calendars. It makes the start of the Iranian calendar, while the Indian calendar starts on March 21 or 22, one or two days after the equinox.

Some religious commemorations also have ties to the spring equinox. The Jewish Passover begins on the first full moon after the equinox. Easter, meanwhile, falls on the first Sunday after the first full moon on or after the equinox in many Christian denominations.

Ancient astronomers in many cultures marked the motion of the sun and worked the equinox into their lives.

Stonehenge is probably the most famous pagan ruin in the popular imagination. Though there is still a lot of mystery surrounding who built it and why, parts of the site line up more or less with the sunrise on the summer and winter solstices, suggesting an astronomical purpose.

Regardless, its popularity as a pagan site usually packs in the crowds at the time of the solstices and equinoxes. For the spring equinox, modern pagans celebrate the festival of Ostara, symbolizing rebirth, renewal and fertility.

Stonehenge's architects weren't the only ones who knew how to build according to the motion of the sun in the sky.

Image: ATSZ56/Wikimedia Commons

The pyramid up above is the Temple of Kukulkan at Chichen Itza in Mexico's Yucatan peninsula. Built by the Maya people, excellent astronomers whose calendar is world-famous, they aligned it such that a trick of the light rewards anyone who happens to be there on the day of the equinox.

Along the length of the steps leading from the base of the pyramid to the summit, the light on the equinox is meant to evoke Kukulkan, the feathered snake diety in the Mayan pantheon.

SOURCE: Time and Date | International Business Times | Calendar in the Sky