(Intro)

The first day of spring is a really special day, and not just because it's when we start thinking about flowers blooming and the days warming up and birds coming back from their winter home.  It's because the first day of spring is also when something special happens.  Something called an equinox.  Isn't that such a cool word?  But what does it mean?  Well, before we can understand exactly what an equinox is, we'll need to learn a little bit about the Earth, specifically, how the Earth moves.

Even though you don't feel it, the Earth is always moving.  In fact, it's moving in two different ways.  First, right now, the Earth is moving around the Sun like this.  It takes a whole year for the Earth to go around the Sun one time, and secondly, at the same time, the Earth also spins around in place, like this.  If you've ever played with a toy top, then you know that the top spins around its center.  So does the Earth.  It spins around an imaginary line that we call the axis.  The Earth's axis runs up and down this way, right through the North Pole and the South Pole.  But the Earth's axis isn't exactly straight up and down.   It's tilted just a little bit.  So, for most of the year, one half of the Earth is tilted toward the Sun and the other half of the Earth is tilted away from the Sun, and that little bit of tilt makes a lot of difference down here on the ground.  That's because the half of the Earth that's tilted toward the Sun gets more direct sunlight, which means it's warmer there and the days are longer.  When that half of the Earth is tilted toward the Sun as far as it can go, it's summer there, and at the same time, the half that's pointing away gets less direct sunlight, so the days are shorter and colder and there, it's winter.

Now, as the Earth moves this way around the Sun, the top half and the bottom half of the Earth change which way they're tilting.  After a few months, the part that was tilting toward the Sun starts to tilt away, and the part that was leaning away starts to lean towards it.  This whole cycle, with the different parts of the Earth getting more and then less direct sunlight throughout the year, is why we have seasons, but there are two times a year when neither side of the Earth is pointing toward the Sun.

Halfway between when one half is tilted toward the Sun and when the other half is tilted away from the Sun, the part that's getting the most direct light from the Sun is right in the middle.  Around the middle of the Earth, there's an imaginary line called the equator, and when the equator is getting the most direct light from the Sun, then both halves of our planet get the same or equal amounts of light, and hey, equal kinds of sounds like equinox, and on equinox, everything is kind of in the middle.  Temperatures are often warmer than they were in the winter but not as warm as they will be in the summer, and the days are longer than they were in the winter but not as long as they're going to get in the summer.  Sounds like this describes spring perfectly.

The spring equinox happens around March 21st and where I live, up here, this part of the Earth starts to tilt more towards the Sun and gets more direct sunlight.  This means we're leaving the colder, shorter days of winter and starting to get the warmer, longer days of spring and summer.  Now, there's another equinox, too.  Because remember I said there are two times a year when neither half of the Earth is pointed toward the Sun.  

After summer is over, the part of the Earth that was leaning toward the Sun starts to tilt away.  Right around September 21st, the most direct sunlight hits the Earth at the equator again, and as that part of the Earth continues to tilt away, it'll head into Autumn and eventually, Winter, but for now, where I live, we're looking forward to our part of the Earth tilting toward the Sun, which means that warmer weather and longer days are on the way.

So until next time, happy spring equinox.  Do you have a question for us?  If you do, ask a grownup to help you leave a comment down below or send us an email to kids@scishow.com.  Thanks and we'll see you next time here at the fort.