Why does solar eclipse occurs on full moon day only ?

A solar eclipse happens when the moon passes between the Earth and Sun, causing people on Earth to be completely or partially unable to see the sun, because the moon is in the way. This is able to happen in spite of the fact that the moon is much smaller than the sun, because while the sun is about 400 times bigger than the moon, it is also 400 times farther away from the Earth than the moon is. The reason that a solar eclipse can only happen during the new moon is that the new moon phase is the only time when the moon is in between the Earth and Sun at all.