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A. Earth
B. Mars
C. Venus
D. Neptune

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Pick one planet and find a picture of it. What is one fact for that planet?

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What is a something fun you have learned? Share any way you want to!

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Using any shape, make the sun, moon, and earth in size comparison to each other. Which is the biggest? Which is the smallest?

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How many moon phases are there? And what do they look like? Find an image to represent the phases.

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Introduction

Moon Phases

In our entire solar system, the only object that shines with its own light is the Sun. That light always beams onto Earth and Moon from the direction of the Sun, illuminating half of our planet in its orbit and reflecting off the surface of the Moon to create moonlight.

This graphic shows the position of the Moon and the Sun during each of the Moon's phases and the Moon as it appears from Earth during each phase. Not to scale. Credit: NASA/JPL-Caltech

Like Earth, the Moon has a day side and a night side, which change as the Moon rotates. The Sun always illuminates half of the Moon while the other half remains dark, but how much we are able to see of that illuminated half changes as the Moon travels through its orbit.

Let's take a look at the individual phases, and how the movements of the Moon and Sun appear to us as we watch from the Northern Hemisphere on Earth:

Our Wobbly Moon

Our Wobbly Moon

When we think of the way the Moon seems to change over the course of a month, we think of phases. But frequent Moon observers know that the Moon also appears to twist, nod, and roll slightly during its journey across the sky, allowing us to peek around the Moon's shoulder and catch glimpses of the farside. This phenomenon is called libration.

Because the Moon's orbit is not perfectly circular, its distance from Earth and its speed in orbit both change slightly throughout the month. The Moon's rate of rotation around its own axis, though, always stays the same.

When the Moon is at its closest to Earth and moving most quickly along its orbital path, the Moon itself doesn't rotate quite fast enough to keep entirely the same side facing us, and we get to see a little more of the eastern side of the Moon. When the Moon is farthest from Earth and orbiting at its slowest, its rotation gets a little ahead, and we see a bit more of its western side. We call this motion "libration in longitude."

The 5 degree tilt of the Moon's orbit also causes it to appear to nod, as though it were saying "yes." The tilt sometimes brings the Moon above Earth's northern hemisphere, and sometimes below Earth's southern hemisphere, allowing us to see slightly more of the northern or southern hemispheres of the Moon. We call this motion "libration in latitude."

Finally, the Moon appears to tilt back and forth like a metronome. The tilt of the Moon's orbit contributes to this, but it's mostly due to the tilt of our Earth. Earth has a tilt of 23.5 degrees on its axis, which means that when we observe the Moon from Earth, it's a little like we're standing sideways on a ramp. If you look left, the ramp slopes up. If you look right, the ramp slopes down. In front of you, the horizon looks higher on the right and lower on the left. If you turn around, the horizon appears to tilt the opposite way.

The tilted ramp works the same as the tilted "platform" of the Earth beneath our feet. Every two weeks, we have to look in the opposite direction to see the Moon, and the ground beneath our feet is then tilted the opposite way as well.

Earthshine

Earthshine

Though the Moon is in a crescent phase in this photograph, most of the darkened, Earth-facing side of the Moon is still dimly visible, illuminated by sunlight reflecting off our planet. This reflected light is called earthshine. Credit: Zolt Levay

Sometimes, when the Moon is in one of its crescent phases, we can still see the darkened area of the Moon's nearside shining dimly. This effect is caused by the Sun's light reflecting off Earth's surface onto the face of the Moon. Because Earth at that point in its orbit is nearly full from the Moon's perspective, the light it reflects, called earthshine, is bright enough to dimly illuminate the darkened surface.

Daytime Moons

Daytime Moons

The waxing Moon rises over a ridge in the Wasatch Mountains, Utah. Credit: NASA/Bill Dunford

Though the Moon is often thought of as a nighttime visitor, it's also visible during the day as a faint, pale presence. The best times to see a daytime Moon are perhaps during the first and last quarter phases, when the Moon is high enough above the horizon and at about 90 degrees from the Sun in the sky. This helps make the Sun's reflected light bright enough to see as it reflects off of the Moon. The Moon can be seen in the daylit sky at any phase except for the new moon, when it's invisible to us, and full moon, when it's below the horizon during the day. The crescent through quarter phases are high in the sky during the day, but the daytime gibbous phases can be glimpsed only just before the Sun sets.

Do It Yourself

Do It Yourself

Spend the next month getting to know the Moon and its phases by filling out your own observation journal.

Have you ever wondered when the next full moon will be? How about the first quarter moon? Put the dates and times for all the Moon's phases for the year at your fingertips by building your own Moon Phases Calendar and Calculator!

Moon phases can be hard to visualize. This simple activity uses a lamp, styrofoam ball and pencil to show how phases work.

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Moon Phases | Phases, Eclipses & Supermoons - Moon: NASA Science

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Everything you want to know about why our Moon's appearance changes throughout the month.

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Starting with the sun, what order do the planets go in moving outward in our solar system?