Phases of the Moon



A diagram which demonstrates why the moon goes through phases.
Click on image for full size (13K GIF)
The diagram shows the Moon in different positions along its orbit around the Earth. The Sun is far away and acts like a light bulb in this picture. Half of the Moon is always reflecting light from the Sun (let's call it the light side), and half of the Moon is always in shadow (the dark side). But that's not all that is happening. Only half of the Moon is facing the Earth so that we can see it (let's call it the near side). The other half is facing away from the Earth (the far side). The phases occur because the near side isn't always the side reflecting light from the Sun.

When the Moon is between the Earth and the Sun (labelled 1), the side of the Moon facing the Earth is the dark side. The Moon cannot be seen. We call this the New Moon because it begins a new cycle of phases. When the Earth is between the Sun and the Moon (5), the side facing the Earth is the light side. We call this Full Moon, even though we can only see half the Moon at one time.

Halfway in between these times (3 & 7), only half of the near side of the moon is reflecting sunlight. So we can only see one-quarter of the Moon. We call these phases First and Third Quarters.

All the phases of the Moon have special names which indicate how much of the illuminated Moon can be seen from Earth, and whether this part is going to grow or shrink.

Galileo's drawings of the phases of the Moon
Lunar eclipses

Nicknames for the Full Moon

Phases of the Moon



A diagram which demonstrates why the moon goes through phases.
Click on image for full size (13K GIF)
The diagram shows the Moon in different positions along its orbit around the Earth. The Sun is off in the distance, lighting the Earth-Moon system. At any position, half of the Moon is illuminated by the Sun (the light side of the Moon) and half is not (the dark side). Also, half of the Moon is visible to the Earth (the near side of the Moon) and half is not (the far side). As the Moon moves around the Earth, we can see different fractions of the illuminated half of the Moon.

When the Moon is between the Earth and the Sun (1), the near side of the Moon is the dark side. The Moon cannot be seen. We call this New Moon, the beginning of a new cycle of lunar phases. When the Earth is between the Sun and the Moon (5), the near side is the light side. We call this Full Moon, even though we only see half the Moon.

Halfway in between these times (3 & 7), only half of the near side of the moon is illuminated by the Sun. So we can only see one quarter of the Moon. We call these phases First and Third Quarters.

All the phases of the Moon have special names which indicate how much of the illuminated Moon can be seen from Earth, and whether this part is going to grow or shrink.

Galileo's drawings of the phases of the Moon
Lunar eclipses

The Many Names for the Full Moon

Phases of the Moon



A diagram which demonstrates why the moon goes through phases.
Click on image for full size (13K GIF>)
The diagram shows the Earth, and the Moon in different positions along its orbit around the Earth. The Sun is off in the distance, lighting the Earth-Moon system. At any position, half of the Moon is reflecting light from the Sun (the light side of the Moon) and half is in shadow (the dark side). Also, half of the Moon can be seen from Earth (the near side of the Moon) and half can not (the far side). As the Moon moves around the Earth, the dark side and the far side overlap and produce the phases of the Moon as we are familiar with them.

When the Moon is between the Earth and the Sun (1), the near side of the Moon is the dark side. The Moon cannot be seen. We call this New Moon, the beginning of the cycle of lunar phases. When the Earth is between the Sun and the Moon (5), the near side is the light side. We call this Full Moon.

Halfway in between these times (3 & 7), only half of the near side of the moon is illuminated by the Sun. So we can only see one quarter of the Moon. We call these phases First and Third Quarters.

All the phases of the Moon have special names which indicate how much of the illuminated Moon can be seen from Earth, and whether this part is going to grow or shrink.

Galileo's drawings of the phases of the Moon
Lunar eclipses

Full Moon Names


Last modified October 19, 2005 by Randy Russell.
The source of this material is Windows to the Universe, at http://www.windows.ucar.edu/ at the University Corporation for Atmospheric Research (UCAR). © The Regents of the University of Michigan. Windows to the Universe® is a registered trademark of UCAR. All Rights Reserved. Site policies and disclaimer