The Phases of the Moon
Objective: To learn about the phases of the Moon
The clearest thing in the night sky is usually the brightly shining Moon.
And every night we see a different face of the Moon.
Sometimes we see a full Moon,
at other times a half Moon
or a crescent Moon,
and sometimes, we don't see the Moon at all.
The Moon is a non-luminous celestial body
and is visible to us only because it reflects the Sun's light.
It is the Earth's natural satellite,
which revolves around the Earth in 27.3 days
and rotates once on its axis in the same period of time.
Its revolution and rotation are such that only one side of the Moon faces the Earth.
As the Moon circles the Earth, we can only see a part of its illuminated portion from the Earth.
The portion of the lit side we see changes.
These changes are known as the phases of the Moon.
When the Moon is between the Sun and the Earth,
its illuminated side faces away from the Earth,
and the side facing the Earth is dark.
At this position,
we do not see the Moon in the sky at all,
and it is called the new Moon or no Moon.
As the Moon moves away from the Sun in the sky,
we see a bit more of the sunlit side of the Moon each night.
A few days after the new Moon,
we see a thin crescent in the sky.
The crescent Moon waxes,
or appears to grow fatter, each night.
When half of the Moon is illuminated, we call it the first quarter moon.
The Moon continues to wax,
and when more than half of it is illuminated, it has a shape we call gibbous.
The gibbous Moon appears to grow fatter each night
until we see the full sunlit face of the Moon.
We call this phase the full Moon.
It rises almost exactly as the Sun sets
and sets just as the Sun rises the next day.
The Moon has now completed one half of the lunar month;
this completion of one half
is also known as waxing of the moon.
During the second half of the lunar month,
the Moon grows thinner each night.
We call this waning.
Its shape is still gibbous at this point, but grows a little thinner each night.
As it reaches the three-quarter point in its month,
the Moon once again shows us one side of its disc illuminated
and the other side in darkness.
However, the side that we saw dark at the first quarter phase
is now the lit side.
As it completes its journey
and approaches the new Moon again,
the Moon is a waning crescent.
After the waning crescent,
we see a new Moon
and the cycle is complete.
The lunar cycle repeats itself every 29.5 days.
To Summarise
The size of the illuminated portion of the Moon, visible from the Earth, varies due to its revolution around the Earth.
These are called the phases of the Moon.
The duration of a lunar cycle is 29.5 days.