Why does the Moon have Phases

The moon does not emit light of its own. Instead, it is illuminated, meaning it reflects light from the sun. As it revolves round the Earth, a person can see the moon in different shapes. At times, the moon may appear full meaning a person can see the whole of it, while at other times, it may appear as a half moon or a thin crescent moon. These different shapes that appear as a result of the amount of light illuminated on the surface of the moon are what are referred to as the phases of the moon.

As the moon revolves around the earth, depending on the surface of the moon that is lighted, its shape usually differs from a full moon when the whole shape of the moon is seen, then decreasing in shapes to a half moon when part of the moon can either be seen in darkness or light, to the point the whole of the moon cannot be seen for it is in total darkness.

“The phases of the moon,” as stated by Woodlands Junior School, “depend on its position in relation to the sun and the Earth. As the moon makes its way around the Earth, we see the bright parts of the moon’s surface at different angles. These are called ‘phases of the moon.’”

Rugusavay explains clearly how the moon phases come about. “As the moon revolves about the earth once in about 29.5 days, we see different amounts of its surface lighted by the sun. When the moon is on the side of the earth away from the sun, we can see all of its lighted half. In other positions around the earth, different amounts of the lighted half of the moon are seen.”

Rugusavay notes an important distinction to what scientists (astronomers) refer to as a new moon opposed to what the rest of us understand by the term ‘new moon.’ “We usually call the thin slice that we see first, the new moon. But scientists call the phase that is not visible from the earth, the new moon.”

When the moon is in the state called the new moon, the moon usually rises close to the same time the sun rises. This also holds true when the sun sets. It sets around the same time the sun sets. However, as days go by, the moon waxes (becoming a crescent moon, a half moon and a gibbous moon on its way to a full moon). During this time the moon rises when the sun has already risen. This signifies when the sun has already set, the moon sets later in the day. When the moon is at the stage called the full moon, the opposite happens. During this time when the sun sets, the moon is rising. Therefore, when the moon sets, the sun is rising.

When the moon wanes (becoming a half moon and a crescent moon on its way to a new moon), the moon rises at night when the sun has already set. This implies the moon will set during daytime when the sun had already risen. The cycle repeats itself back to the new moon then full moon.

Definition of terms used in this article (as defined or explained by Enchanted Learning)

A crescent moon is part way between a half moon and a new moon, or between a new moon and a half moon.

A full moon appears as an entire circle in the sky.

A gibbous moon is between a full moon and a half moon, or between a half moon and a full moon.

A half moon looks like half a circle. It is sometimes called a quarter moon…

The new moon is the phase of the moon when the moon is not visible from Earth, because the side of the moon that is facing us is not being lit by the sun.