Another thing to know to understand the full moon calendar 2021 is to know the moon phases, which are four:
- to new Moon, the moon is located between the Earth and the sun, so that the side of the moon facing us does not receive direct sunlight and is illuminated only by the dim sunlight reflected from the Earth;
- a few days later, as the moon moves around the Earth, the side we can see gradually becomes more illuminated by direct sunlight, with this thin sliver being called crescent crescent;
- a week after the new moon, the moon is 90 degrees away from the sun in the sky and is semi-illuminated, in what we call first quarter because it is located about a quarter of the way around the Earth;
- a few days later, the area of illumination continues to increase and, as more than half of the face of the moon receives sunlight, we arrive at the phase which is called the waxing gibbous moon;
- when the moon has moved 180 degrees from its new moon position, the sun, earth and moon form a line. The disk of the moon is as close as possible to being fully illuminated by the sun, hence this is called full moon;
- subsequently, the moon moves until more than half of its face appears to be receiving sunlight, but the amount begins to decrease, this is the phase waning gibbous;
- days later, the moon moved another quarter of a turn around the Earth, to the position of third fourth, with the sunlight now shining on the other half of the visible face of the moon;
- subsequently, the moon moves into the phase of waning crescent as less than half of its face appears to be receiving sunlight and the amount is decreasing, it eventually returns to its initial new moon position.
Since the moon’s orbit is not exactly in the same plane as Earth’s orbit around the sun, they are rarely perfectly aligned, in fact the moon usually passes above or below the sun from our vantage point, but occasionally passes right in front of sun and we get a solar eclipse.