Why does the moon have different shapes in the sky and what are those shapes called?

Answer 1

The moon has no light of its own and the only reason that we can see it at all is because of light from our sun falling onto the moon and then being reflected back to us.

When the earth lies between the sun and the moon, part of the moon disc will seem to disappear because it lies in the earth's shadow and this is why the moon looks to be different shapes throughout the month.

As the portion of the moon that we can see is getting larger, the moon is said to be "waxing". Once the moon has passed the point where we can see all of it (the full moon) and starts to look smaller, it is said to be "waning".

The names of all of the phases of the moon's cycle are: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, waning crescent.

You can see some images of the moon's phases in the Sources and related links section, below.

Answer 2

The moon appears to have different shapes in the sky due to its changing relationship with the Sun and Earth, known as lunar phases. The shapes, such as crescent, gibbous, and full moon, are named based on how much of the moon's surface is illuminated by the Sun as seen from Earth.