Why does the moon have different phases?

What is a moon phase or lunar phase?

Moon or lunar phase is the different shapes of the moon seen from the earth. The moon itself does not change its shape but the variations in the shape are a result of the illumination of different regions of the moon by the sun.

Why does the moon show different phases?

The reason for this is the different positions of the moon as it orbits around the earth.

Video Source: gyfcat.com

The moon rotates on its axis and also revolves around the earth in an orbit. During this revolution, the moon continuously changes its position relative to the earth's position and due to this change in positions, the region of the moon that gets illuminated by the sun also varies. Therefore, we see different shapes or phases of the moon.

How many moon phases or lunar phases are there?

Image Source: sciencelearn.org.nz

There are 8 phases of the moon.

1. New Moon: This phase of the moon is not visible to the naked eyes. The moon is in between the earth and the sun and the illuminated face of the moon is towards the sun. The only time a new moon can be seen with the naked eyes is during a solar eclipse.

2. Waxing Crescent: A thin portion of the moon is visible.

3. First Quarter: Half of the moon is visible.

4. Waxing Gibbous: More than half of the moon is visible.

5. Full Moon: The whole bright side of the moon is visible and it appears as a glowing sphere. The earth is in between the moon and the sun.

6. Waning Gibbous: The illuminated region of the moon starts to decrease from here. The waning crescent phase is just like the waxing crescent phase but reversed.

7. Third Quarter: Half of the moon is visible.

8. Waning Crescent: Only a thin portion of the moon is visible. It is the last phase of the lunar cycle and is followed by the new moon.

It takes 29.5 days for the moon to complete one lunar cycle.

After reading about the types of moon phases and especially about the new moon and full moon, you might be thinking

Why do we not see a solar eclipse and lunar eclipse every month if the moon is between the earth and the sun during the new moon phase and the earth is between the sun and the moon during the full moon phase?

The simple answer to this question is because of the tilt in the moon's orbit.

The earth revolves around the sun in an orbit and the moon revolves around the earth but both the orbits are in different planes. It is because the orbit of the moon is tilted about 5.15 degrees from the orbit of the earth. So, even if the moon is in the new moon phase and lies between the earth and the sun, it is because of this 5° tilt that there is no solar eclipse and the same is with the lunar eclipse also. The picture below makes it clear.

Image Source: Hyperphysics There is a certain condition for the formation of solar and lunar eclipses. There will be a time when the orbit of the moon will intersect the plane of the orbit of the earth and at that time if the moon is in the new moon phase or full moon phase, a lunar eclipse or solar eclipse will be formed.