August 21st is going to be an insane day across the United States as millions of people gather along a thin line that stretches from coast to coast to watch the moon pass directly in front of the sun in a total solar eclipse.
Only those along that line will see totality — when the moon blocks the sun perfectly — but it is worth making the effort to get to it. I know, because I’ve seen five of them.
The Earth is the only planet in our solar system with a moon that is exactly the right size and distance from us, so that when it passes in front of the sun, it covers the sun exactly. Other planets have moons that pass in front of the sun as well, but they are either too small or too far away from their planet to cover the sun completely.
For example, in 2013, the Curiosity rover on Mars caught Phobos, one the two moons orbiting the red planet, passing in front of the sun, revealing the potato-like shape of the little moon, but it only covered part of the solar disc.
Our much larger moon is still 400 times smaller in diameter than the sun, but the sun happens to be 400 times farther away, so from where we stand, they both appear to be exactly the same size in the sky. This cosmic coincidence gives us the spectacle of a total eclipse, and this summer will be the first one to track right across the United States in almost a hundred years.
While many people in Canada will see part of the sun covered during the event, only those along the centre line, which is a little over 100 km wide, will get the full effect. And that effect is spectacular.
Pictures of totality usually show the sun as a black disk with an ethereal halo around it called the corona. This is the atmosphere of the sun that reaches out millions of kilometres into space and is actually hotter than the surface of the…