This week 6-year-old Kambreigh Schooley asked us why she can sometimes see the moon during the daytime…What a great question!
To answer this question you need to first remember that one half of the moon is always illuminated by the Sun.
As the Moon travels around Earth in its 29 day orbit, the portion of the illuminated half of the moon that is visible to us is always changing, creating the different moon phases as we see in the diagram below.
Moonlight is light from the sun bouncing off of the moon and reflecting back to us on Earth. It’s very bright! Full moons are the brightest moons because virtually all of the illuminated portion of the moon is visible to everyone on the night-time side of Earth. First Quarter and Third Quarter moons only show us half of the sunlight side of the moon.
Because nighttime moonlight is so bright and beautiful it’s easy to overlook the fact that moonlight is also bright enough to be easily seen against the blue sky during the day.
Now back to the question about why the moon is sometimes visible above the horizon during the daytime hours. Take another look at the moon phase chart above. Imagine yourself standing at the various locations on Earth indicated by the time of day.
You can see that at the 12 o’clock noon position, you’re directly under the Sun, and if you happen to be looking up on the day of the New Moon, you’ll not only be looking toward the Sun, you’ll also be looking in the direction of the dark half of the moon. Not much fun there.
Now imagine yourself at that noon location on Earth, but the moon’s phase is either First Quarter or Third Quarter. Can you see the moon? Sure! Your line of sight permits you to see the moon quite well, even though it’s daylight.
It’s generally been my experience that the best time to try daylight observations of the moon is in the week following Full Moon. Look in the west or southwestern skies during the mid-morning hours. If the skies are clear, you’ll have no trouble seeing the moon, in broad daylight.