When the moon comes in between the Sun and the Earth, and all three are in a straight line, then it is
Solar Eclipse
On a certain moon’s day, the moon happens to come in between the Sun and the Earth. Also, the centers of the Sun, the moon, and the Earth are in a straight line. In such a situation, the moon being smaller in size casts its shadow only on a limited region of the Earth. In these regions of the Earth, the solar eclipse occurs.