ON 8 APRIL, a total solar eclipse will be visible from various parts of North America. The path in which this will occur runs from Mexico, diagonally across the US and into the Atlantic region of Canada. Eclipses like this, where the moon moves directly between the sun and Earth and blocks out light, happen almost every 20 years. But our planet is a big place, and these events can’t be seen everywhere. Only about once every 400 years is one visible from any given spot on Earth. Which is to say, those of us in or near the…