In astronomy, an eclipse occurs whenever celestial bodies are aligned so that the sight of one of them is destroyed because of this alignment.
Of course the moon is much smaller than the sun, which would prevent it from cover it. It turns out that, as the distance of the moon and the earth to the sun is very large what we see is only an illusion that they are both the same size. So much so that when the moon is at the farthest point of its orbit (which is an ellipse) it does not even cover the sun completely, is called annular eclipse.
There are three types of eclipse: total eclipse, when the sun is completely covered by the moon; the partial eclipse, when only part of the sun is hidden by the moon; and the annular eclipse, when the moon is far from the earth in its orbit and can cover only the center of the solar disk.
Importantly, an eclipse only occurs when the moon is new or full moon in the moon phase.
