Why does the Moon have phases

A phase of the moon is its current sunlit portion that is in view of the ones who are looking at it from the earth (in the general sense). Depending on each of the lunar phases, the moon can appear to be of different shapes and sizes. The phases of the moon changes periodically and it is a cyclical process that has been going on since the moon came into existence and it is based on the movements of itself, the earth and the sun.

What one needs to understand is that in actuality, the portion of the moon that faces the sun at that time is always lit (14.77 days) and the other half that is not, is always dark (14.77 days). This fact however, is not what we observe from the earth because when one looks up at the moon from the earth, the visibility depends on the day itself. One can see the entire moon (perfectly round, dish like) on a full moon night, while on a new moon night; one will not be able to see any moon at all.

Among the misconceptions about the reasons behind the changing phases of the moon, is the one about the earth’s shadow (umbra). Lunar phases do not change due to the falling of the shadow of the earth on the moon; if that happens, it is known as a lunar eclipse. The sunlit portion which would be visible to us will depend on the alignment of the three celestial bodies concerned, the sun, the earth and the moon itself. For example, if the sun and the moon are on the exact same side of the earth, we cannot see the moon, because at that time, we are facing the aforementioned dark side of the moon and the side of the moon that is facing the sun and not the earth is getting all the light. Similarly, when the moon and the sun are on exact opposite sides of the earth; we can see the entire sunlit face of the moon (full moon). The positions or phases in between are all a result of the constantly moving celestial bodies as they change their position from one to the next. In order to further explain the different levels of visibility of the moon, the main changes in its phases are discussed below.

New Moon -– As explained above, the moon becomes totally invisible as the earth, the sun and the moon align with each other.

Waxing Crescent Moon –- The second phase of the moon lasts until the satellite reaches about 49% visibility and is most prominent during the afternoon and after dusk.

First Quarter Moon –- This is the time when the moon appears to be an exact half-circle from the afternoon to early hours of the night.

Waxing Gibbous Moon –- This phase continues just until the Full Moon appears in the sky, and it remains particularly visible from late afternoon to almost the whole night.

Full Moon -– The visibly complete round phase of the moon that can be seen all night long from sunset onwards.

Waning Gibbous Moon -– Immediately following the Full Moon, the waning gibbous moon can be seen for days during the wee hours of the morning and almost the whole night, until the moon’s visibility becomes exactly half again.

Third/Last Quarter Moon -– One can see the half-circle like moon once again from late night till the first hours of the morning.

Waning Crescent Moon -– It is the last visible phase of the moon and can be seen best, just before dawn.

Dark Moon -– The last day of the lunar cycle and this phase is invisible to the naked eye.