With a total eclipse of the Sun less than a week away, let’s consider why solar eclipses happen.
A solar eclipse can occur only at the time of the new moon. The Moon appears to us in phases, and the principle phases are new moon, first quarter, full moon, and third (or last) quarter. Those phases are dependent on the relative position of the Sun, Moon, and Earth. The entire sequence of phases takes about 29.5 days, which is a synodic (or lunar) month. The new moon is the time when the Moon and the Sun are on the same side of the Earth.
Obviously, if the Moon is on the side of Earth where the Sun is, we can’t see the Moon at night. It also means we usually can’t see it during the day because the Sun’s brightness hides it except when the Moon passes in front of the Sun. When the Moon only partially blocks the Sun, we see a partial eclipse. When the Moon is precisely aligned with the Sun, we see a total eclipse.
During a total eclipse, the Moon casts a moving shadow over a portion of the Earth. Those who are outside of that shadow can still see a partial eclipse. How much of the Sun is hidden by the Moon depends on how far the viewer is from the shadow. People all over North America will see the eclipse that is coming as a partial eclipse. It will only be total for those who are in the 70-mile-wide path of the shadow that will travel from Oregon to South Carolina.
The fact that the Moon can completely cover the much larger Sun, as it will do in the coming eclipse, has been described as a “marvelous coincidence.” We think God planned it that way. Tomorrow we will tell you why solar eclipses with the Moon exactly covering the Sun are important.
–Roland Earnst © 2017