Why do we sometimes see the Moon during the day?

We mostly associate our lunar companion with nighttime. But it's often visible in the sky during the day as well. Here's how it all works.

Transcript

00:00How come we sometimes see the moon during the day?

00:06We mostly associate our lunar companion with night time, like the stars.

00:11We can't see them during the day because of our own star, the sun.

00:17When its rays strike the gas molecules that make up our atmosphere,

00:21they scatter radiation in the shortwave part of the spectrum, the blue part.

00:26That reflected radiation drowns out the dim light emitted by the distant stars,

00:32but it doesn't drown out the moon.

00:36Like Earth, our natural satellite doesn't emit any light of its own,

00:40but sunlight always lights up half of it, a hemisphere.

00:45Because the moon is much closer to us than other celestial bodies

00:49and reflects so much of the sun's light,

00:52it can often be seen during the daytime if conditions are right.

00:58Earth completes a full rotation on its axis once a day.

01:04Meanwhile, the moon is circling the Earth,

01:06but it takes almost a month to orbit us.

01:10And as it moves from full moon to new moon and back,

01:13the fraction of lit hemisphere we can see changes a little every day.

01:18At first it grows, waxing until it's full.

01:22That's when the moon is opposite the sun in relation to Earth.

01:26The entire lit hemisphere is visible from here, full moon.

01:32Then it starts to wane as its lit hemisphere slowly turns away.

01:37Eventually the moon is between the Earth and the sun.

01:40With the lit side facing away from us, it seems to disappear.

01:44New moon, it's still in the sky.

01:49Just don't expect to see it either at night or in the day

01:53until it begins to wax again on its endless journey around Earth.

02:00The best time to see our satellite during daytime hours

02:04is when it's a first quarter or last quarter moon,

02:08what people often call a half moon.

02:10During those phases, it's bright and high above the horizon

02:15for many hours of the day.