Why is this eclipse so special?

Today we took possession of our rented motor home.  Departure for the great American mid-west tomorrow!

There is growing excitement as we make contact via our host’s facebook account with a small group of travellers who are converging along with Sylvie and me onto this point of totality from various neighouring states. No Canadian countrymen yet.  I just had a pleasant phone conversation about strategies for observing with an engineer in Boulder who, like me, seeks to bring his family away from the crowds and traffic that they’re anticipating around major population centres.

There is an eclipse somewhere on Planet Earth about once every 18 months or so.  To put it another way, every 17 out of 18 times the Moon comes between  Sun and Earth, its shadow cone skirts above or below the Earth and on that  18th time, the shadow sweeps across the top, the bottom, or the middle of the planet, giving a total solar eclipse to a narrow band of turf anywhere from 100 to 200 km wide depending on how close the Moon is in its elliptical orbit.  Sometimes the cone of the Moon’s shadow narrowly misses the Earth, and part of the Earth gets only a partial eclipse where the Moon is seen to skirt across the top or bottom of the Sun without completely covering it. In a partial eclipse the Sun appears as a crescent from the observer’s viewpoint (as seen through solar filters or by projection through a pinhole camera or téléscope). But when a total eclipse occurs, there is always a wide swath of Earth on either side of the shadow track where the eclipse is partial.  In our hometown of Quebec City, 61% of the Sun will be eclipsed by the Moon.

This eclipse is special because it is the first one to touch the USA since February 1979 when the Moon’s shadow swept across the Pacific NW and on into Canada across North Dakota’s northern border.   This eclipse will be total across the  continental USA from Pacific to Atlantic.  It crosses a fairly densly populated part of the world in the age of the internet, cellphones and citizen reporting via live view on social media.

Here is a video I made Sunday afternoon.  I hope it makes it easier for the reader to understand how easy it is for Sun, Moon and Earth to frequently avoid perfect alignment.