Did anyone notice the Moon last night? Just after sunset, the Moon would have looked something like this.

What you would see is known as "Earthshine". Earthshine is the light of our own planet shining down on the Moon's dark terrain. It makes a ghostly image of the full Moon inside the horns of the crescent. Five hundred years ago, Leonardo da Vinci was first to explain this phenomenon, and so it is sometimes called the "da Vinci glow."

A crescent Moon with Earthshine is one of the prettiest sights you'll see in the night sky. Step outside just after sunset, and look toward the west.