Understanding the phases of the Moon

5 April

During the course of a month, the Moon goes through several phases. The major Moon phases are the new moon, the first quarter, the full moon, and the third quarter. As a matter of fact, the Moon displays eight main phases. We'll dive deeper into these phases to find out why this Earth's most constant companion changes its appearance night after night.

Understanding the phases of the Moon

Lunar phases are the shapes of the visible part of the satellite from Earth's perspective. Fun fact: the illuminated edge of the Moon's visible surface is called the limb, while the line that separates the illuminated and the shaded sections is the Moon's terminator (a word derived from the Latin "terminare", which means "to set bounds to").

As the Moon goes around the Earth, the Sun illuminates different parts of the Moon, which changes its appearance and creates lunar phases.

Examples of terminology relating to lunar phases that is commonly used by the scientific community:

The Moon cycle, which is one full orbit by our Moon around the Earth. It takes 29.5 days.
A Synodic month, or a Lunation, being the time between two successive new moons.
The age of the Moon, which is the number of days since the last new moon.

A guide to the phases of the Moon

There are 4 major phases of the Moon — the full moon, the new moon, the first and the last quarters. The 4 minor phases are waxing crescent, waxing gibbous, waning gibbous, and waning crescent. The major phases of the Moon occur about 7.4 days apart.

New moon

The Moon is between the Sun and the Earth. Thus, the side of the Moon facing the Earth is in shadow.

Waxing crescent

This phase follows the new moon, as the Moon starts to "grow". We only see the edge of the part that is gradually illuminated by the Sun.

First quarter

The Moon has completed 1/4 of its orbit around the Earth. Half of the Moon's surface is illuminated by the Sun.

Waxing gibbous

More than half of the Moon’s surface visible from Earth is illuminated.

Full moon

During this phase, the Earth is positioned between the Moon and the Sun, which illuminates the entire near-side of the satellite. We can enjoy the round appearance of the full moon all night long.

Waning gibbous

After the full moon, the illuminated part of the Moon begins to wane. During this phase, the surface of the Moon that we see from the Earth is still mostly illuminated.

Last quarter

The Moon looks like it is half illuminated.

Waning crescent

The final phase of the Moon before transitioning back into the new moon. Only a small, crescent-shaped sliver of the Moon is visible, which is diminishing in size.

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Understanding the phases of the Moon