Lunar Phases

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The Moon doesn’t shine on its own—it reflects light from the Sun. So, when the Moon orbits Earth, we see different parts of the lit side, which creates its phases.

The cycle begins with the New Moon phase when the Moon is between Earth and the Sun. We can’t see the Moon because its lit side faces away from us.

As the Moon moves further around the Earth, a sliver of light appears. This is called the Waxing Crescent phase.

When half the Moon’s face is lit, it’s the First Quarter. As days pass by, the Moon keeps getting brighter!

During the Waxing Gibbous phase, more than half the Moon’s face shines.

Around 15 days after the New Moon, the entire lit side faces Earth, leading to the spectacular Full Moon.

After this, the Moon’s lit surface starts to shrink. The Waning Gibbous is followed by the Last Quarter, then the Waning Crescent, and finally, the cycle starts over with the New Moon.

These phases repeat in a 29.5-day cycle as the Moon orbits around Earth.

Overview

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Lunar Phases

The Moon does not produce its own light but instead reflects sunlight. As the Moon orbits Earth, different portions of its illuminated side become visible from Earth, creating the lunar phases. The complete cycle of lunar phases takes approximately 29.5 days. It includes eight distinct phases: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, and waning crescent. Understanding lunar phases helps scientists track time, predict tides, and study the movement of celestial bodies.

Science and Engineering Practices (SEP): Developing and Using Models

Scientists develop and use models to explain and predict the changing phases of the Moon. Since the positions of the Sun, Earth, and Moon determine the phases, models help visualize how the Moon’s appearance changes over time. These models illustrate why the same phase does not appear every night and how the cycle repeats each month. By refining these models, scientists can better predict lunar phases and understand their effects on natural systems, such as ocean tides.

Activity Ideas:

Modeling moon phases using cookies – Use cookies with white cream inside to model the eight main phases of the Moon. Carefully twist apart each cookie and shape the cream to match each phase – new moon, waxing crescent, first quarter, waxing gibbous, full moon, and so on. Label each one and place them in the correct order.
Observing the Moon – Keep a daily record of the Moon’s shape for one month. Compare your observations to a lunar phase calendar to identify patterns in the cycle.

Crosscutting Concept (CCC): Cause and effect

The Moon's changing appearance is caused by its orbit around Earth and the way sunlight illuminates its surface. Scientists can predict lunar phases and their effects on Earth by understanding these interactions.

Cause: The Moon orbits Earth while sunlight illuminates one side.
Effect: As the Moon moves, different portions of the lit side become visible, creating a predictable cycle of lunar phases.
Cause: The same side of the Moon always faces Earth.
Effect: We always see the same surface of the Moon, but its lit portion changes as it moves.
Cause: The Moon’s phases follow a regular 29.5-day cycle.
Effect: Scientists can predict when each phase will occur and how it will impact Earth’s tides and night sky visibility.

Procedure

Transcript

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