Whether it feels or looks like spring or like winter outside your home today, spring is officially here. It slipped under my pillow while I was still asleep this morning at 6:28 am ET here in the Northern Hemisphere.

Our ancestors my not have understood what was happening to our planet from a celestial viewpoint, but they were more careful observers of the world around them and definitely marked today as something significant. Ancient observers built devices, buildings and places like Stonehenge to measure and mark changes in the Sun’s movements. Of course, that was what they thought was happening – that the Sun was moving closer or further from Earth. They may have been wrong on that part, but they were able to mark that today was midway between the sun’s lowest path across the sky in winter and highest path across the sky in summer.

Though we visualize an equinox as occurring on the imaginary dome of Earth’s sky, it is a very real point on Earth’s orbit that is halfway between the two extremes of the sun’s path in your sky. “Your sky” because though the equinox occurs at the same time for all of us. The seasons are based on whether you are in the Northern or Southern Hemisphere.

One thing you can observe easily at each equinox (no Stonehenge required) is that the sun rises due east and sets due west from where you live. An equinox happens when the ecliptic – or sun’s path – intersects the celestial equator, that imaginary line above Earth’s equator.

Go outside around sunset and sunrise and notice the location of the sun on the horizon with respect to local landmarks. You can then use those landmarks to find those cardinal directions in the months ahead and observe how the sunrise and sunset points move southward or northward. I showed my young sons this many years ago by crudely tracking the sunrise moving from window to window during the year from the vantage point of our East-facing family room. It was a pretty interesting lesson in science.

Today the sun is on the celestial equator. It may be springlike outside or it may still seem like winter, but the new season has arrived.