# data[].attributes.body
Have you ever looked into the sky at night and seen that the moon looked a little different? This is because of the Moon phases! The Moon travels around our Earth in what is called an "orbit". The Earth also orbits around the sun.
Because the Moon and Earth are always orbiting, we see only certain parts of the moon at a time. The sun lights up parts of the moon to create "phases" and that is what we see when we look up at the sky! Some phases show the moon completely like a full moon, while others show a tiny bit, like a crescent.

# data[].attributes.body
Moon phases are the illuminated portions of the Moon that can be seen from Earth. Changes made to these illuminations are caused by the Moon's orbit around the Earth, and the Earth's orbit around the Sun. Since the Moon orbits at a 5-degree angle around the Earth, the Moon's phases look different over time.

# data[].attributes.headline
Earth's Place in the Universe: Standard 1-ESS1-1

# data[].attributes.subject
Earth's Place in the Universe: Standard 1-ESS1-1

# data[].attributes.body
Use observations of the sun, moon, and stars to describe patterns that can be predicted.

# data[].attributes.body
1st Grade, aligning with Louisiana State Standards

# data[].attributes.attachment_link.readable_text
Using discrepant events to confront misconceptions

Next to the Sun, the Moon is the most luminous object in the sky. It is visible on most clear nights and often during the day as well. Most students know that the Moon has phases, but rarely understand why these phases occur. Middle-level students most commonly suggest that the phases of the moon are caused by the Earth's shadow ( Driver et al. 2015), though sometimes the shadows of other planets, clouds, and even the Sun are thought to cause the phases of the Moon ( Dunford and Jones 2019). In fact, the Moon is illuminated by the Sun in much the same way as the Earth-that is, one side of it is continuously in the path of the Sun's rays. However, as the Moon orbits the Earth, observers standing on the Earth's surface can see more or less of the Moon's illuminated surface ( Figure 1), giving the appearance of phases.

This month's Disequilibrium column explores how to help students refine their mental models about the phases of the Moon-an important component of MS-ESS1-1 ( NGSS Lead States 2013)-using a kinesthetic demonstration that challenges the notion that the Earth's shadow causes the Moon's phases.

Project three pictures of the Moon on a whiteboard in various phases (bonus points if these are photos you've taken yourself, near a local landmark!). Ask students why the Moon looks different throughout the month, and then ask them to make drawings to explain this phenomenon. Specify that students draw a view from space that is a considerable distance away so that the Earth and Moon (and perhaps the Sun) appear in the drawing. After a few minutes, have students compare their drawings with others in the class, and ask groups to share a few of the ideas from their drawings. Be prepared to hear a diverse, possibly wild, set of ideas. Driver et al. (2015) found that at the middle level, some students still do not think the Earth orbits the Sun, so you can imagine how this might filter into a diagrammatic model of the Moon's phases.

Explore: The Moon Walk!

Tell students that the drawings they just created and compared were a kind of model of the Moon's behavior. Now, they are going to learn about how the Moon's phases work using another kind of model-a physical model (adapted from NASA's Jet Propulsion Laboratory [JPL], 2010) in which they will be a part of the system.

To represent the Sun in the model, place a bright, uncovered 100-watt lamp in the middle of the room. Then, take out a white Styrofoam ball (two to three inches in diameter is fine) with a pencil or dowel rod stuck into the ball, like an oversized lollipop. Tell students that the ball will represent the Moon and the pencil is a convenient way of holding it without your hand getting in the way of the Moon. Tell students that their heads will represent the Earth and that their eyes will give the viewpoint from Earth. In this model, the Moon will orbit the Earth, and we will recreate the apparent phases of the Moon. Divide the class into a few groups and give each group one model Moon. Materials allowing, you could give a model to pairs or even individual students. Just make sure that students have enough space for what follows.

To begin, darken the room except for the "Sun." Write "Day 0" or the date of the most recent new Moon on the board. Instruct students to face the lamp from various places around the room and extend the model Moon directly in front of them, at about eye level ( Figure 2). Safety note: Tell students not to look directly at the Sun/bulb. Students will see only the dark face of the sphere, equivalent to the new Moon (the Moon on Day 0 of the cycle). Ask students to identify where the shadow of Earth is during this phase-it will not fall on the Moon, but behind them. Have students draw or take photographs of this phase of the Moon.

Next, repeat the process at the following points, each time writing a new day or date on the board, and asking students to identify where the Earth's shadow is at each phase.

Day 4: Have students turn their bodies 45° counterclockwise, still holding the Moon out in front of their faces. They will see that a crescent-shaped sliver of the Moon is illuminated, while the rest remains dark. It is worth pausing here to ask students what is represented by this turn in their bodies. Students may think turning represents the rotation of the Earth-emphasize that it is actually the Moon revolving around the Earth, a process that takes about 28 days.

Day 8 (first quarter Moon): Have students turn 90° counterclockwise from their original position.

Day 14 (full Moon): Have students turn 180° from their original position. Note here that the Earth's shadow is cast toward the Moon, which is why lunar eclipses can happen during full Moons. However, if students are holding their models at about eye level, their own shadows should not be cast upon their model Moons (<a class="fig" href="#SS_40_F3">Figure 3</a>).

Day 21 (third quarter Moon): Have students turn to 270° counterclockwise from their initial position.

Day 28/Day 0: Have students slowly rotate counterclockwise to a full rotation, watching what happens to the Moon as they complete the cycle.

When the Moon is visible during the day, you can bring the Styrofoam balls outside, hold them toward the Moon, and see that they will be illuminated by the Sun in the same proportion as the visible Moon (see Resources). This is most feasible when the Moon is in the first- or third-quarter phases; first-quarter Moons are generally visible in the east during the afternoon, while third-quarter Moons are visible in the mornings in the west (see Resources to get more information on the moonrise and moonset in your area).

Ask students to identify, in their own words, the patterns they saw during the demonstration, and to describe the reasons for the phases of the Moon. Follow up with a video that describes the Moon's phases in more technical terms-fifth and sixth graders may enjoy BrainPop's video on the topic (sign in required), while PBS and Crash Course jointly host a slightly longer video for older students (see Resources).

Because the Moon has been an object of human interest for so long, activities about its phases are never in short supply. Here are a few possibilities!

History connection: Have students research some of the earliest calendars humans ever created, most of which were based on the Moon. There are also some modern lunisolar calendars, which students might find interesting to report on.

Model analysis: Probe more deeply into the ways the model used in the Explore section is accurate and inaccurate. The model, for instance, is not to scale, nor does it show the inclination of the Moon's orbit. Ask students to design a model that corrects (some of) these inaccuracies and describe its pros and cons.

Lunar eclipses: Ask students to explore the NASA videos demonstrating how the Earth's shadow does cause lunar eclipses on rare occasions (see Resources). Then ask students how the model used in Explore could be modified to illustrate this. This is a fun extension, but be warned: lunar eclipses are not an easy idea to grasp and may require a full lesson (or more) to clarify.

Solar eclipses: Solar eclipses are a rare and spectacular phenomenon, caused by the shadow of the new Moon. The United States will experience a total eclipse on April 8, 2024. Can our simple Moon model be made to show how solar eclipses happen, too? As with lunar eclipses, this is a complex but fascinating extension, ideal for students who need more challenging material. (See Resources for more information on solar eclipses.)

Finally, project the photos you showed at the beginning of class once more. Ask students to create a new and improved diagrammatic model showing how each of these phases are possible.

Conclusion

These activities give students repeated opportunities to engage with models illustrating various facets of the Sun-Moon-Earth system, which address the content, science practices, and crosscutting concepts associated with MS-ESS1-1 ( NGSS Lead States 2013). Working with causal models of this sort can contribute to effective science teaching ( Windschitl, Thompson, and Braaten 2018), and may allow your students to reason much more clearly about light and shadow in the solar system.

References

Driver R., Rushworth P., Squires A., and Wood-Robinson V.. 2015. Making sense of secondary science: Research into children's ideas. Abingdon, UK: Routledge.

Dunford B., and Jones A.. 2019. About the Moon: Misconceptions. NASA. .

Jet Propulsion Laboratory (JPL). 2010. Moon phases demonstration (lesson plan). NASA. .

NGSS Lead States. 2013. Next generation science standards: For states, by states. Washington, DC: The National Academies Press. .

Windschitl M., Thompson J., and Braaten M.. 2018. Ambitious science teaching. Cambridge, MA: Harvard Education Press.

Brain Pop Science-

Lunar Eclipses and the Moon's Orbit- NASA-

Maps of the 2024 total eclipse-

Moonrise and Moonset lookup-

PBS video-

The Moon's Role in a Solar Eclipse-

Why does the moon have phases?-

# data[].attributes.attachment_link.description
Using discrepant events to confront misconceptions Next to the Sun, the Moon is the most luminous object in the sky. It is visible on most clear nights and often during the day as well. Most students know that the Moon has phases, but rarely understand why these phases occur.

# data[].attributes.attachment_link.description
Kids learn about the science of the phases of the moon. Full, Gibbous, Quarter, and crescent.

# data[].attributes.attachment_link.readable_text
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.

# data[].attributes.attachment_link.title
Moon Phases | Phases, Eclipses & Supermoons - Moon: NASA Science

# data[].attributes.attachment_link.description
Everything you want to know about why our Moon's appearance changes throughout the month.

# data[].attributes.headline
Resource #5: Data- Moon Phase Calendar 2022

# data[].attributes.subject
Resource #5: Data- Moon Phase Calendar 2022

# data[].attributes.attachment_link.readable_text
What's the Moon's phase tonight? With our 2021 Moon Phase Calendar, you'll find when the next new Moon, first quarter, full Moon, or last quarter is happening-for all 12 months of 2021. AND our tool is customized to YOUR zip code. No converting to your local time! We also provide daily Moon illumination percentages and the Moon's current age.

See Moon phases for all 12 months of 2021-plus, you can go backwards or forwards in time to find out the full Moon or Moon phases from 1902 to 2037!

Also, learn more about Moon phases and the meanings behind common terms such as "lunar cycle," "waxing gibbous," "earthshine," "perigee," and more.

Related links:

Moon Phase Calendar September 2021

All times in Eastern time.

About the Moon's Phases

What Are Moon Phases?

As the Moon orbits around Earth and Earth orbits around the Sun, the angle between the Sun, Moon, and Earth changes. As a result, the amount of sunlight that reflects off the Moon and travels to our eyes changes every day. (The Moon itself produces no light of its own.)

We see the Moon's disk change from all dark to all light to all dark again: This span of time is called a lunar cycle, lunation, lunar month, or synodic month. The length of the cycle can vary slightly, but on average, it is 29.53059 days. (See "What's the Moon's Age?" below for more information.)

Astronomers have broken down this cycle into four primary Moon phases: New Moon, First Quarter, Full Moon, and Last Quarter. There are also four secondary phases: Waxing Crescent, Waxing Gibbous, Waning Gibbous, and Waning Crescent. The primary phases occur at a specific moment, no matter where you are on Earth, which is then converted to local time. (Depending on where you live, you may or may not be able to see the exact moment of a phase, in part because the Moon may not have risen yet in your area.) The secondary phases, however, represent a span of time rather than a specific moment.

* New Moon

This phase is named as such because it starts a new lunar cycle. At this time, the Sun and Moon are in conjunction, meaning that they are closest together in the sky, on the same side of Earth (Sun→Moon→Earth). From our perspective, the Moon appears totally dark: We can not usually see it because we are facing the Moon's shadowed side, which does not receive any direct sunlight. But if we were to travel to the other side of the Moon, the part that faces the Sun, it would be totally illuminated.

Occasionally, if the new Moon's position lines up correctly between the Sun and Earth, from our viewpoint it will cover part or all of the Sun's disk, causing a solar eclipse. These events are only visible from a small portion of Earth and require special eye protection to be viewed safely. ( Read more about solar eclipses here!)

The months of some calendars, such as the Chinese lunisolar calendar, begin at the time of the new (or dark) Moon.

* Waxing Crescent

This phase occurs between the new Moon and first quarter phases. At the beginning of this stage, we see a thin, crescent-shape Moon, which, in the Northern Hemisphere, appears on the right side. The lit area slowly widens each day, covering more and more of the right side of the Moon's surface until the first quarter phase, when the Moon's entire right side is illuminated. (In the Southern Hemisphere, the same thing happens, only on the left side.)

Some lunar and lunisolar calendars, such as the Islamic (or Hijri) calendar, define the start of a month as when the Moon first becomes visible, which is usually a day or so after the new Moon, during its waxing crescent stage.

* First Quarter

This phase got its name because at this point the Moon has traveled 1/4 of the way through its orbit. It's a confusing label, though, because at this time from our perspective, 1/2 of the Moon's surface is lit. In fact, both the first and last quarter phases are sometimes called a Half Moon. At first quarter in the Northern Hemisphere, the right side of the Moon is illuminated; in the Southern Hemisphere, it's the left side. In actuality, we are seeing 1/2 of the lit side of the Moon because the entire illuminated surface is only partly facing our direction. In other words, the Moon is perpendicular to the Earth/Sun line. During a first quarter phase, the Moon is said to be at east quadrature, meaning that it is 90 degrees east of the Sun when viewed from Earth.

* Waxing Gibbous

This phase occurs between the first quarter and full Moon and describes the Moon when it is more than half lit, but not yet fully. At the beginning of this stage in the Northern Hemisphere, we see the right half of the Moon illuminated plus a tiny fraction more extending into the left side. As the days pass, the light creeps farther left, covering more and more of the Moon's surface until the full Moon phase, when the entire disk is illuminated. In the Southern Hemisphere, the same happens, only from left to right.

"Gibbous" comes from a Latin word meaning "humpbacked," referring to the curved lit area on the Moon's surface.

* Full Moon

This phase is named as such because, from our perspective, the full disk is illuminated. At this time, the Sun and Moon are in opposition, meaning that they are farthest apart in the sky, on opposite sides of Earth (Sun→Earth→Moon).

Occasionally, if the full Moon's position lines up correctly with the Sun and Earth, from our viewpoint, the Moon will enter Earth's shadow, which will cut off part or all of the sunlight reflected off the Moon's surface, thereby causing a lunar eclipse. ( Learn more about lunar eclipses here!)

* Waning Gibbous

This phase occurs between the full and last quarter and describes the Moon when it is more than half lit, but not fully. At the beginning of this stage in the Northern Hemisphere, we see a disk almost fully lit except for a tiny sliver on the right side that is in darkness. As the days pass, the lit area shrinks from right to left until the last quarter phase, when the Moon's left half is illuminated and the right half is in darkness. In the Southern Hemisphere, the same happens, only the light shrinks from left to right.

* Last Quarter

This phase got its name because at this point the Moon has traveled 3/4 of the way through its orbit, and has just one more (the last) quarter to complete one revolution. This stage is sometimes also called Third Quarter. At this stage, we see 1/2 of the Moon's surface lit. In the Northern Hemisphere, the left side is illuminated; in the Southern Hemisphere, it is the right side. During a last quarter phase, the Moon is said to be at west quadrature, meaning that it is 90 degrees west of the Sun when viewed from Earth.

* Waning Crescent

This phase occurs between the last quarter and new Moon phases. At the beginning of this stage, in the Northern Hemisphere, we see the Moon's entire left side almost fully lit and the right side in darkness. The lit area slowly shrinks each day, covering less and less of the Moon's surface until it looks like a very thin crescent on the left side. Eventually, the entire disk will be in darkness, at which point it will be the new Moon phase and another lunar cycle will have begun. (In the Southern Hemisphere, the same thing happens, only the lit area would have started on the right side and shrunk from left to right, until a thin crescent remained on the right.) Once the Sun rises, it is not easy to see this slim phase; the best time is before the glare of sunrise.

What Is the Moon's Age?

The term " Moon's age" is not a reference to how long the Moon has existed (about 4.5 billion years, if you're wondering), but rather how many days it's been since the last new Moon. As mentioned above, the span of time between one new Moon and the next is called a lunar cycle, lunation, lunar month, or synodic month and on average lasts for 29.53059 days. This translates to 29 days, 12 hours, 44 minutes, and 3 seconds.

For most dates in the above Moon Phase Calendar, there is listed at the bottom of the grid cell a number of days, such as "18 days." This tells us the amount of days since the previous new Moon, or in other words, how many days into the lunar cycle we are-aka, the Moon's age. So, at the new Moon, that day is "0" (not labeled); the next day, 1 day has passed; and onward until 29 days pass and we are at the next new Moon. You can also find this information in the print edition of The Old Farmer's Almanac, in the last (right) column of the Left-Hand Calendar Pages.

The length of a lunar cycle can vary by more than 13 hours due to a few factors. For example, when the new Moon phase occurs at about the same the time as perigee (the point in the Moon's elliptical orbit that is closest to Earth), shorter lunations result. When the new Moon phase occurs at about the same time as apogee (when the Moon is farthest from Earth), longer lunations result. This is related to the fact that the Moon travels faster in its orbit at perigee and slowest in its orbit at apogee.

Earth's relative position near perihelion (point in Earth's orbit that is closest to the Sun) and aphelion (when Earth is farthest from the Sun) also affect lunation times. The longest lunations result when the new Moon coincides with apogee and Earth is at perihelion. The shortest lunations result when the new Moon coincides with perigee and Earth is at aphelion.

One of the shortest lunations was 29 days, 6 hours, and 35 minutes, whereas one of the longest was 29 days, 19 hours, 55 minutes.

Note: The synodic month describes the time for the Moon to complete one orbit around Earth and return to the same position relative to the Sun and Earth. If Earth were not moving along in its orbit but instead were standing still, the Moon would take less time to reach that same position: This is called the sidereal month, which is about 2.21 days shorter than the synodic month. "Sidereal" means "related to stars"-in this case, the Moon's position relative to the stars.

What Is Percent Illumination?

Percent illumination, listed in the Moon Phase Calendar under the Moon symbol, tells us how much of the Moon's disk is lit, as seen from Earth. Looking at the calendar on this page, you can see that from new to full, the percentage increases, indicating the waxing stages, and from full to new, the percentage decreases, indicating the waning stages. The New Moon is 0 percent illuminated (or totally dark); First Quarter is essentially 50 percent illuminated (half of the disk is lit); Full Moon is 100 percent illuminated (the entire disk is lit); and Last Quarter is back to essentially 50 percent illuminated (half of the disk is lit).

We say "essentially" for the quarter phases because technically, at the exact time of the first quarter, a tiny fraction more than half of the Moon is lit, and at last quarter, a tiny fraction less. The Moon is exactly half-lit when it reaches dichotomy, which occurs several minutes before first quarter and several minutes after last quarter.

When Does the Moon Rise and Set?

Below are general guidelines as to where to look for the Moon during each of its phases. Times mentioned are solar time, not clock time. The four primary phases (in italics) rise and set at a point in time; the four secondary phases occur over a broader timespan.

Phase

Rises Near the East

Highest in the Sky

Sets Near the West

Waxing Crescent

Between sunrise and noon

Afternoon

Between sunset and midnight

Waxing Gibbous

Between noon and sunset

Evening

Between midnight and sunrise

Waning Gibbous

Between sunset and midnight

Early morning

Between sunrise and noon

Waning Crescent

Between midnight and sunrise

Morning

Between noon and sunset

What Is Earthshine?

Earthshine is sunlight that dimly illuminates the dark part of the Moon's surface that faces us. It occurs when light travels from the Sun to Earth, reflects off the Earth, travels to the Moon, and then bounces back to Earth to reach our eyes. When this happens, we can see part of the Moon that normally isn't lit, but this portion is much dimmer than section directly illuminated by sunlight.

For example, during a waxing crescent stage, we might see a thin crescent brightly lit by direct sunlight, but also the rest of the Moon's disk slightly illuminated by a much dimmer glow from earthshine. Sometimes this appearance is called the "old Moon in the new Moon's arms."

Earthshine is most noticeable within five days of a new Moon (during the waning and waxing crescent stages).
Browse Moon Phases and Lunar Calendars by State or Province

# data[].attributes.attachment_link.title
Moon Phase Calendar | What is the Moon Phase Today?

# data[].attributes.attachment_link.description
What is the Moon Phase today? Use our Moon Phase Calendar to find dates and times of the full Moon, new Moon, and every phase in between. Beyond the phases of the Moon, you will also see daily Moon illumination percentages and the Moon's age.

# data[].attributes.body
After sending this email, Kevin informed me that while he did not know of the information I was searching for, he would be able to provide me with a link to multiple STEM resources corresponding to Space Science. The link to those resources is as follows: https://www.nasa.gov/stem/foreducators/k-12/index.html