By Will Dunham WASHINGTON (Reuters) – The moon will completely blot out the sun for millions of people in North America along a path crossing from Mexico into the United States and then Canada in a total solar eclipse occurring on April 8. Here is an explanation of the solar eclipse and where it will be visible. WHAT IS A TOTAL SOLAR ECLIPSE? In a total solar eclipse, the moon passes between the sun and Earth, entirely covering the face of the sun along a small path of our planet’s surface. This is called the “path of totality.” The daytime sky turns dark, akin to dusk or dawn, and nocturnal a…