Moon to the Eclipse:
7/23/17 New Moon

New moon (This photo was actually taken just after the official new moon. It shows the moon’s lighted side peeking around the edge again.)
Photo by NASA

The new moon seems absent from the sky. It’s now positioned between us and the Sun, its far side fully illuminated by the Sun and the side facing us in full shadow.

This month, and most months, the moon’s orbit passes above or below the Sun, so it isn’t directly between the Sun and Earth. But next month, on August 21, the moon’s orbit will place it perfectly between the Sun and us. The three bodies will line up, and the moon will block the Sun from our view. Then, we’ll see the new moon in spectacular fashion as its disk—that black, shadowed side—passes in front of the Sun.

As the moon approaches the Sun before an eclipse, it shows us its shadowed side, so it’s invisible against the daytime sky. We don’t see it coming, which makes its sudden silhouette biting into the Sun even more startling.

Consider the monthly lunar cycle in relation to solar eclipses. As the moon circles Earth, and the Sun lights the moon causing us to see its phases, it’s inevitable that a solar eclipse occurs only during a new moon. Whenever we see only the dark side of the moon—a new moon--it’s because the moon is between the Sun and us. And that is the very cause of an eclipse.

(next post in our Moon to the Eclipse series)

The moon orbits the Earth about once a month. As it circles our planet, we see different amounts of the lighted and dark sides of the moon. The blue boxes mark today’s moon.
Orbit illustration by Karl Tate, SPACE.com, from NASA. Moon phase photos by Fred Espenak.