The Moon always has the same side facing the Earth. Although it does not produce light itself, it is illuminated by the Sun to varying degrees during its orbit around the Earth. This is observable to us as the phases_of_the_Moon.
When the Moon is positioned between the Earth and the Sun, the light from the Sun illuminates the side, which is turned away from the Earth. The side that is usually visible to us is not illuminated at all during this period, making the Moon invisible. This is what we call a New Moon.
Several days later the Moon is seen as a crescent over the western horizon. When it has completed a quarter of its orbit around the Earth we can see the western or right side of the Moon.
As the orbit continues, an increasing portion of the side facing the Earth is illuminated. Finally we see a Full Moon, which is when the entire side facing the Earth is illuminated.
Only a few days after that, the shape of the Moon changes again. The dark part increases and we speak of a waning Moon. When the Moon has completed three quarters of its orbit, only half of the side facing the Earth is still illuminated. At this time the Moon is only visible during the second half of the night.
A short time before the next New Moon, we can observe a narrow crescent in the east of the morning sky. Finally, the Moon is invisible again and we have a New Moon.
Each Moon cycle from new Moon to full Moon to new Moon takes 29 days, 12 hours, 44 minutes and 2. 8 seconds. During the period from new Moon to full Moon, the Moon is said to be waxing, while it is said to be waning during the period from full Moon to new Moon.
A lunar eclipse is a quite spectacular phenomenon. It occurs approximately every six months. Usually the Moon passes above or below the shadow_of_the_Earth, as its path is at an angle of about 5 degrees to that of the Earth.
A partial eclipse of the Moon is observed when part of the Moon lies in the core_shadow of the Earth. If the Moon is completely inside the Earth's shadow and is not visible at all, it is termed a total eclipse of the Moon. The most recent total eclipse was observable in Europe, Asia and America on the 21st January 2000.
