The different ways the Moon appears from Earth during a month is known as the phases of the Moon. The moon does not have any light of its own. The light that we see from the surface of the moon, is the reflection of the sun's light. The positions of the Earth, Moon, and Sun vary throughout the course of the month. As we are aware that the Moon orbits around the Earth, the half of the Moon that faces the Sun will be lit up.

The different shapes of the lit portion of the Moon that we see from Earth are known as phases of the Moon. Each phase repeats itself every 29.5 days.

We see a full moon, when the surface of the side of the moon facing Earth is completely illuminated. The phase when, none of the surface of the moon is lit up and we can’t see the moon at all, is a new moon phase. When half the side of the moon is visible from the Earth, the phases are called the first and third quarters. When the visible moon appears to be getting bigger, we say the moon is waxing; and when the visible lighted surface seems to be getting smaller, we say the moon is waning. When less than half of the moon is visible, it’s called a crescent, and when it’s more than half, it’s called a gibbous.

The phase of the moon that are visible to us, depends on where the Earth is relative to the Moon and the Sun. The phase when the Moon is between the Earth and Sun, the illuminated surface of the moon is not facing us, and we can’t see the moon at all, it is the new moon. When the Earth is between the Moon and the Sun, the light of the sun bounces off the surface of the moon, and the moon is completely lit up, seen from earth, we call it the full moon. When the Moon is between those two positions, we see the first and third quarter.

Astronomers across the globe, have observed the phases of the moon for thousands of years and have concluded that it takes 29 and a half days for the moon to go through its entire phase cycle. This is known as a lunar month. 

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NGSS

MS-ESS1-1.

MS-ESS1-2

MS-ESS1-3

ESS1.A

ESS1.B

3.PS2.A (MS-ESS1-1),(MS-ESS1-2); 5.PS2.B (MS-ESS1-1),(MS-ESS1-2); 5.ESS1.A (MS-ESS1-2); 5.ESS1.B (MS-ESS1-1),(MS-ESS1-2),(MS-ESS1-3); HS.PS2.A (MS-ESS1-1),(MS-ESS1-2); HS.PS2.B (MS-ESS1-1),(MS-ESS1-2); HS.LS4.C (MS-ESS1-4); HS.ESS1.A (MS-ESS1-2); HS.ESS1.B (MS-ESS1-1),(MS-ESS1-2),(MS-ESS1-3); HS.ESS2.A (MS-ESS1-3)

Common Core State Standards Connections: