When the moon is between the sun and earth what determines if a solar eclipse occurs?

Answer 1

Solar eclipses occur when the Moon and Sun lie on the same line of sight from the standpoint of a terrestrial observer. Naturally, there are two types of solar eclipses: partial and total. The Sun and Moon have about the same angular size (they take up the same amount of area on the celestial sphere as seen from Earth), so in order to have a total eclipse, the alignment of Sun, Earth, and Moon must be just right for the right observer.

It is also worth noting that the Moon's shadow is not as big as the Moon; it shrinks proportional to the square of the distance between it and whatever object it's casting its shadow upon (in this case, the Earth).

Total solar eclipses are both very rare and subjective. That is to say that there is only a small area on the Earth where one can observe a total solar eclipse when one occurs. Others will see a partial eclipse.