“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%.
The Moon and Sun each take up approximately half a degree on the sky as viewed from Earth. When the Moon is slightly larger in angular size than the Sun is and all three bodies perfectly align, a total solar eclipse is the result. Image credit: Romeo Durscher / NASA / Goddard Space Flight Center.
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 — ...