As the Moon orbits around the Earth, the half of the Moon that faces the Sun lit up, the different shapes of the lit portion of the Moon can be seen from Earth and known as phases of the Moon. Each phase repeats itself every 29.5 days.
The same half of the Moon always faces the Earth, because of tidal locking (synchronous rotation or captured rotation). Tidal locking is when one side of an astronomical body always faces another.
Difference between New Moon and Full moon is around 15 days.
What is New Moon (Amavasya) ?A new moon is when the Moon cannot be seen because we are looking at the unlit half of the Moon. The new moon phase occurs when the Moon is directly between the Earth and Sun, a solar eclipse can only happen at new moon.
What is Full Moon (Poornima) ?A Full Moon is when we can see the entire lit portion of the Moon. The full moon phase occurs when the Moon is on the opposite side of the Earth from the Sun, called opposition, a lunar eclipse can only happen at full moon.
Shukla pakshaShukla paksha refers to the bright lunar fortnight or waxing moon, it is a period of 15 days, which begins on the Shukla Amavasya (New Moon) day and culminating Purnima (Full Moon).
Krishna pakshaKrishna paksha refers to the dark lunar fortnight or waning moon, it is a period of 15 days, which begins on the (Full Moon) day (Purnima), culminating on (New Moon) day (Amavasya).
Lunar eclipseA lunar eclipse can only occur at Full Moon, and only if the Moon passes through some portion of Earth's shadow.
This can occur only when the Sun, Earth, and Moon are exactly or very closely aligned, with Earth between the other two.
That shadow is actually composed of two cone-shaped components, one nested inside the other. The outer or penumbral shadow is a zone where the Earth blocks part but not all of the Sun's rays from reaching the Moon. In contrast, the inner or umbral shadow is a region where the Earth blocks all direct sunlight from reaching the Moon.
1) Penumbral Lunar EclipseThe Moon passes through Earth's penumbral shadow. These events are of only academic interest because they are subtle and hard to observe.
2) Partial Lunar EclipseA portion of the Moon passes through Earth's umbral shadow. These events are easy to see, even with the unaided eye.
3) Total Lunar EclipseThe entire Moon passes through Earth's umbral shadow. These events are quite striking due to the Moon's vibrant red color during the total phase (totality).
A blood moon happens when Earth's moon is in a total lunar eclipse. While it has no special astronomical significance, the view in the sky is striking as the usually whiteish moon becomes red or ruddy-brown.