If you’re living in the Northern Hemisphere you’re probably over winter by now. Daylight saving time has kicked in, but it’s still so damn cold even another hour of sunlight won’t get you out of bed. But don’t worry, you won’t be sulking in your Snuggie for too much longer.

Today is the March or vernal equinox, better known as the first day of spring. As this month progresses you’ll slowly start to notice warmer weather, longer days, and people walking outside with shorts on. But what exactly is the Earth doing to cause these seasonal changes? It’s all in our planets tilt.

Our planet revolves around the sun at a slight angle — roughly 23.5 degrees to be exact. This little lean is responsible for all four of our seasons. So when the Northern Hemisphere is tilted away from the sun it’s winter up here, but it’s summer for everyone down in the Southern Hemisphere.

Image taken from page 216 of 'La Terra, trattato popolare di geografia universale per G. Marinelli ed altri scienziati italiani, etc. [With illustrations and maps.]'
Earth orbits the sun at a tilt, giving us our four seasons.

The March equinox is a transitional period when the Northern Hemisphere begins to lean towards the sun, ushering in spring.

At approximately 12:15 p.m. Eastern on March 20, the sun will shine directly on the equator. This means there will be almost equal amounts of day and night across the globe, for a moment we will be in between seasons.

For those in the Southern Hemisphere this means it’s time to dust off your coats, while those of us in the northern half of the world will be breaking out our bathing suits.

For most people this yearly occurrence isn’t that big of a deal unless you’re truly paying attention to the position of the sun in the sky. But ancient civilizations, like the Mayans, revered the March equinox so much they built temples and shrines that would indicate when it was occurring.

The Mayan pyramid in Chichen Itza, Mexico, known as El Castillo, was constructed at the perfect angle to indicate exactly when the equinox was happening. Twice a year for about half an hour a sliver of light shines down one of the temple’s staircases in the shape of a serpent’s body. At the bottom of the stairs lied a carved head of the Mayan snake god, Kukulkan. Whenever this stone deity was fully illuminated the Mayans knew change was upon them.

So while the equinox might not be as much of a monumental event for us today, it’s still a ubiquitous time of change for all people. Hopefully it’s enough change to get you out of that Snuggie and onto the beach.