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What Are the Phases of the Moon?

Using Slooh’s Online Telescope and integrated NGSS aligned Quest learning activity, you can learn more about the lunar phases while capturing your own images of each one. The Mystery of the Changing Moon is one of 60+ curriculum-aligned STEM Quest learning activities on Slooh for students 4th grade to college.

Slooh’s Online Telescope:

If you are an educator looking for fun, interactive ways to teach NGSS: MS-ESS1-1, as well as other standard curriculum codes related to astronomy, keep reading to the end for more information on The Mystery of the Changing Moon Quest and ways to easily integrate Slooh into your classroom.


The Lunar Phases

From the perspective of the Sun, the Moon always looks the same as it orbits the Earth – the half of it facing the Sun is always lit while the half facing away is always dark. However, the same is not true from the perspective of the Earth. Each of the different appearances of the Moon over the course of the lunar month (29.5 days) is called a lunar phase, and each phase has a unique name.

New Moon:

Total Solar Eclipse

The first phase is the New Moon, which occurs when the Moon is on the same side of the Earth as the Sun, between the Earth and the Sun. During this phase, the Moon is out during the day and is too close to the sun to be visible from Earth.

The Moon does not orbit the Earth on the same plane in which the Earth orbits the Sun. The Moon’s orbit is tilted about 5 degrees, making it slightly above or below the Earth’s orbital plane most of the time. When the Earth, Moon, and Sun are aligned perfectly in the same plane, an eclipse happens! During a New Moon, a solar eclipse can happen, in which the Moon’s shadow covers the Sun, temporarily blocking out light during the day.

One interesting aspect of orbits is that they are not perfectly circular, they are more of an oval shape. The mathematical term for that is an ellipse. The consequence of this shape is that sometimes the Moon is closer to us and other times it is further away. A remarkable coincidences is that the Sun and the Moon are about the same size in the sky, despite being vastly different distances and are not at all similar in size.

When the Moon is further away from us during a solar eclipse, it does not quite cover the entire Sun, instead forming a ring around the outline of the Moon. This is called an annular solar eclipse. When the Moon is closer, it covers the entire disk of the Sun. This type of eclipse is called a total solar eclipse. It makes the Sun’s corona, the outermost part of the Sun’s atmosphere, visible.

Waxing Crescent Moon:

The Waxing Crescent Moon appears two to three days after the New Moon. At this point, the Moon has moved far enough away from the Sun to appear in the evening twilight skies. During this phase, only a small portion of the side of the Moon that faces us is illuminated, and you can see it right above the western horizon shortly after sunset. It is considered a young Moon because only a small portion of the side of the Moon that faces us is illuminated.

If you look closely, you may notice that you can still faintly see the entire disk of the Moon, which is the entire surface of the Moon facing us. What is going on here? Not only does sunlight reflect off the Moon and come towards Earth, the opposite also happens. Sunlight reflects off the Earth’s atmosphere and towards the Moon, slightly illuminating the entire Moon! This phenomenon is called earthshine.

First Quarter Moon:

As the Moon continues its monthly orbit around the Earth, it reaches a position where it forms a right angle to the Earth and Sun, illuminating its eastern side. This position is known as the First Quarter Moon. From our viewpoint, it looks like half of the Moon we see is illuminated during this phase – but astronomers call this a First Quarter Moon to remind us that the Moon is one-quarter of the way through the lunar month.

Waxing Gibbous Moon:

The Waxing Gibbous Moon is the next phase. “Gibbous” refers to a phase that falls between the quarter and full lunar phases, while “waxing” means more of the Moon’s surface is being illuminated each night. This phase occurs when the Moon has moved far enough away from the Sun that more than half of the side facing the Earth is illuminated. It rises in the evening before sunset and sets before dawn.

Full Moon:

The Full Moon is the midway point in the lunar month. The Moon is on the opposite side of the Earth from the Sun, so it is visible all night long, rising at sunset and setting at sunrise! Strangely, this phase isn't a great time to observe the Moon. That's because no shadows are being cast on lunar features, meaning there is little contrast or detail visible.

Remember how a solar eclipse can happen during a New Moon? Well, when the Sun, Earth, and Moon align on the same plane during the Full Moon, a lunar eclipse happens! In a lunar eclipse, the Moon drifts into Earth's shadow. Lunar eclipses are the only times that less than half of the Moon is illuminated by sunlight. However, something remarkable can happen during a lunar eclipse. Sunlight refracts, or passes through, the atmosphere and deflects blue light away while directing red light towards the Moon, causing it to look red!

Total Lunar Eclipse

Waning Gibbous Moon:

The Waning Gibbous Moon is another “gibbous” phase, when less than all but more than quarter of the Moon from our viewpoint is illuminated, but this time it is “waning”, meaning that less of the Moon is illuminated each night. This phase happens when the Moon is starting to move closer to the Sun, and more than half of the side facing the Earth is illuminated. It rises in the east after sunset and sets in the west after sunrise.

Last Quarter Moon:

During the Last Quarter Moon, the Moon once again forms a right angle to the Earth and Sun, this time causing the western side to be illuminated. This phase is unlike the gibbous and crescent phases because it only happens at one specific moment in the lunar month.

Waning Crescent Moon:

The Waning Crescent Moon is the last of the lunar phases, rising later and later each night. Although it is only visible near the end of each night, lots of detail can be seen along the terminator, the region between the lit and unlit portions of the Moon.

Primary and Intermediate Phases

The eight phases can be divided into two groups: primary and intermediate. Primary phases happen at one specific moment each lunar month, while intermediate phases occur over the periods of time between the primary phases. The primary phases are the New Moon, First Quarter Moon, Full Moon, and Last Quarter Moon. The remaining four phases are all intermediate phases.

The Dark Side of the Moon

The Moon rotates on its axis at the same rate at which it orbits Earth, so the same side of the Moon is always facing us. This is the side that we see illuminated to different extents depending on the lunar phase. The other side is sometimes referred to as the dark side, although what we really mean is the far side, as it receives the same amount of sunlight as the side facing us does over the course of the lunar month. The side of the Moon that's always facing us is referred to as the near side.

Lunar Phase Calendar

Now that you know what each lunar phase is, check out the calendar below to see when each one will occur for the rest of 2022!


More About Slooh’s The Mystery of the Changing Moon Quest

When you think of the Moon, you probably think of the magnificent Full Moon. This is how we are used to seeing our Moon depicted in photographs. But have you noticed that the appearance of the Moon changes? Do you think there is a pattern to these changes?

Learning Objectives

By the end of this Quest, students will be able to answer the following questions:

  • What causes the cyclic pattern of the lunar phases every month?

  • What is an orbit?

  • What are eclipses, and why don't they occur every month?

Vocabulary Words

Standards Addressed

NGSS Performance Expectations



RST.9-10.1, RST.9-10.2, RST.9-10.4, RST.9-10.5, RST.9-10.9, RST.9-10.10, WHST.9-10.2.D, WHST.9-10.2.E, WHST.9-10.2.F​

Related Slooh Quests

  1. Mama Killa, Inca Moon

  2. The Moon - Lunar Features

  3. In the Footsteps of Apollo Astronauts

More About Slooh’s Astronomy NGSS Aligned Learning Activities

Slooh’s Online Telescope is a learning platform designed to support any educator in teaching astronomy to meet NGSS requirements by collecting and analyzing real-world phenomena. No previous experience with telescopes is necessary to quickly learn how to use Slooh to explore space with your students.

You can join today to access Slooh's Online Telescope and all 60+ Quest learning activities if you are able to make astronomy a core subject of study for the semester or year. If you only have a few weeks to study astronomy, we also have a curriculum designed to fit your busy academic schedule and budgetary limitations. To learn more about our offers, click here.


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