Tomorrow marks the vernal equinox: 12 hours of light and 12 hours of dark as those of us in the northern hemisphere transition out of winter and into spring. But what makes this equinox exceptional? The supermoon solar eclipse, of course!

Usually a supermoon is a full moon. We notice it then because it looks so much bigger than it usually does–and that’s because it is closer to Earth. How does it come closer? The moon doesn’t orbit our planet in a circle, but rather in an elongated shape called an ellipse. That path puts the moon closer to our planet during some points in its orbit and farther away during others. And just like a car driving by, it appears smaller from a distance and really big close up.

Today, the moon is close (making it a supermoon), but it’s a new moon. That means the moon is between Earth and the sun. The sun’s light doesn’t shine on the side we can see, so it seems as though there’s no moon at all.

Most of the time, the new moon isn’t directly between the sun and the Earth. But sometimes its orbit takes it right across the face of the sun, blocking out the sun’s light. We call that a solar eclipse.

Those of us in North America won’t be able to witness this special event, since it will happen during the night. Folks in Europe will see a partial eclipse (the moon will cover some, but not all, of the sun). But if you happen to find yourself in a boat east of Iceland, you can bathe in the moon’s shadow as you celebrate spring.

Did you know? During a supermoon, the moon is 50,000 kilometers (31,000 miles) closer to Earth than it is when it reaches the most distant point in its orbit.