Phases of the Moon

PHASES OF THE MOON

How the sun illuminates the moon in different locations around Earth
Figure from http://www.moonconnection.com/moon_phases.phtml

The lunar phases of the Moon are based on the Moon’s position relative to the Sun around the Earth. In the photo above you can see that the Sun illuminates the Moon at all times, but we don’t see the full Moon everyday because it is in different positions around the Earth. It takes the Moon 29 ½ days to complete each cycle of the lunar phases, but only takes 27.3 days for it to orbit around the Earth. The roughly two day difference is due to the fact that the Earth is also orbiting the Sun at the same time that the Moon is orbiting the Earth and therefor it needs those two extra days to catch up to the Earth's new location in the orbit.

Full Strawberry Moon in June
Figure from www.space.com

FUN FACT: The word “month” was formed by the term “moonth” because each complete cycle of the lunar phases takes about 29 ½ days.

Since the cycle takes around a month to complete that means that there is a full moon every month. Here are some fun facts regarding that concept:

FUN FACT: Each Full Moon of the year has its own name based off of the month that it falls in. For example, the Full Moon in June is called the Strawberry Moon and the Full Moon in April is called the Pink Moon.

FUN FACT: About every 19 years the month of February does not have a Full Moon.

When the Moon is closest to the Sun (between the Sun and the Earth) it is called a New Moon and is not visible on Earth. This is because the Sun is illuminating the side of the Moon facing it and from Earth we see the backside of the Moon. When the Moon is furthest from the Sun (the Earth in between) we see the Full Moon because the Sun illuminates the side of the Moon that is facing towards the Earth. When the Moon goes from New Moon to Full Moon it is considered “waxing”, meaning that it is increasing in visibility, and when it goes from Full Moon to New Moon it is considered “waning”, meaning that it is decreasing in visibility. The phases just before and after the New Moon are referred to as “crescent” and the phases just before and after the Full Moon are referred to as “gibbous”.

The Moon’s phases are also directly related to where it rises and sets. A Full Moon rises at sunset and sets at sunrise, whereas a New Moon rises at sunrise and sets at sunset making it not visible. The moon also sets later each night, allowing the waxing phases to be visible in the afternoon and early evening and the waning phases to be visible in the late evening and early morning. 

All the phases of the moon
Figure from http://astropixels.com/ephemeris/phasescat/phasescat.html

A common misconception is that there is a "dark side" of the moon, when in actuality the Moon is rotating so every part of the Moon is illuminated at some point during the phases. Another idea people often aren't aware of is that we only see one side of the Moon because the Moon orbits the Earth and rotates fully one time per orbit. This is called synchronous rotation. To see a demonstration of this concept I would recommend watching this Youtube video:
https://www.youtube.com/watch?v=OZIB_leg75Q

Occasionally when the Moon, the Sun, and the Earth all fall together in a straight line there is an eclipse. For more information about eclipses check out Tabreya's blog post here:
http://as151.blogspot.com/2016/09/how-does-moon-cut-his-hair-eclipse-it.html