Moon to the Eclipse:
7/30/17 Quarter Moon

Quarter moon, waxing
Photo by NASA

After last week’s new moon, when the moon’s shadowed side faced Earth and we saw nothing of its lighted side, it has now circled away from the Sun in its monthly orbit. Tonight if you look at the moon you’ll see half of its lighted side and half of its dark side—a quarter moon.

In a month’s cycle, there are two different quarter moons. This one, the first after the new moon, is called the First Quarter; the other is the Third or Last Quarter. Compare the two and you’ll notice that the shadow is on a different side for each. An animation of the changing moon shows why. The shadow seems to move from right to left across its face as the moon grows (waxes) and then shrinks again (wanes). As seen from Earth’s northern hemisphere, the waxing quarter moon is always shadowed on the left.

In the next days, watch as the shadowed side rotates away from us on the way to another full moon next week.

(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.