Key difference: A new moon occurs when the Moon is between the Earth and the Sun. A full moon occurs when the Moon is on the far side of the Earth from the Sun.

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While, we all have seen a full moon and a new moon, in addition to the other various moon phases, some might not know why or how this happens. After all, the moon is always there, right, so how come we can only see part of it?

First, let’s see what a full moon and new moon are. A full moon is when the whole moon is visible in all its glory. Whereas, a new moon, also called the dark of the moon is when no part of the moon is visible from the Earth. Both a full moon and new moon are phases of the moon, in addition to waxing crescent moon, first quarter moon, waxing gibbous moon, waning gibbous moon, third (last) quarter moon, and waning crescent moon. See the difference between planets and moons.

A lunar phase is the “appearance of the illuminated (sunlit) portion of the Moon as seen by an observer, usually on Earth.” This occurs as the Moon orbits the Earth. The reason for the various appearances is the changing relative positions of the Earth, Moon, and Sun. The moon appears as a full moon when the Sun and Moon are on opposite sides of the Earth. It appears as a new moon when the Sun and Moon are on the same side of Earth. The phases of a full moon and new moon occur when the Earth, Moon, and Sun lie approximately in a straight line.

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The moon does not have the light of its own; it instead reflects the light off the sun. Half of the lunar surface facing the Sun is always sunlit. However, at any given time from Earth, parts of the moon can be visible, depending on where the moon is at its orbit around the Earth. These can vary from 0% (new moon) to 100% (full moon). A new moon occurs when the Moon is between the Earth and the Sun. A full moon occurs when the Moon is on the far side of the Earth from the Sun. See Dwarf Planets Vs. Moons

The moon goes through a cycle of its phases every month. It takes approximately 29.5 days to complete this cycle. This period of 29.53 days is called a lunar month. The concept of the calendar month is derived from the lunar month. In fact, the word ‘month’ is derived from ‘moon.’ The month starts with the new moon up to the full moon, which halfway through the lunar month, i.e. the 15^th day. Then it goes back to the new moon, at which time, the cycle begins anew.

Phases of the moon through the lunar month: New Moon – Waxing Crescent Moon – First Quarter Moon – Waxing Gibbous Moon – Full Moon – Waning Gibbous Moon – Third (Last) Quarter Moon – Waning Crescent Moon – Dark Moon.

Also see: Difference between dwarf planets and asteroids

Image Courtesy: powerss.ism-online.org, aa.usno.navy.mil