“We live in a moment of history where change is so speeded up that we begin to see the present only when it is already disappearing.” -R. D. Laing
This coming Monday, tens of millions of people will gather to watch the total solar eclipse that will go coast-to-coast across the continental United States. Total solar eclipses like this happen, on average, about once every 18 months, due to the frequency of alignment as well as the Moon’s apparent angular size. At present, about 40% of all solar eclipses are total eclipses, with annular eclipses making up 50% and hybrid eclipses the other 10%.
However, this ratio has changed with time, and will continue to change. The Moon is migrating farther away from Earth, and annular eclipses are becoming more common, while total eclipses are becoming more rare. Although the migration rate is small — mere centimeters per year — that adds up over millions of years. At some point in the future, the Moon’s shadow will be completely unable to fall on Earth’s surface any longer.