Eclipse take place when te sun, the moon and the earth lies on a same straight line. However, the orbits of the earth and the moon do not occur in the same straight line in every new moon and full moon. An angle of 5.15° is formed between the orbital plane of the moon and the orbital plane of the earth. therefore the eclipse is not possible. The sun, the moon and the eath intersect in two places, which are called nodes. These nodes are called rehu and ketu. The sun, the moon and the earth should be in the nodes for eclipse to occur, which is not possible in every full moon and the new moon. Therefore, eclipse does not occur in every new moon and full moon.