Followup: Supereclipse

I wrote earlier about the annular eclipse happening this coming Sunday. It's a solar eclipse, with the Moon blocking the Sun, but because the Moon is at apogee -- the point in its orbit farthest from Earth -- the Moon appears smaller in the sky, so it doesn't completely block the Sun. We're left with a ring of solar surface surrounding the Moon, the so-called Ring of Fire. I got a couple of people asking me why this eclipse is happening at lunar apogee when we just had a "Supermoon", when the Moon was full at perigee (when it's closest to Earth in its orbit). This is a good question! It's not a coincidence. In fact, it must happen this way! Here's why. First, here's a drawing of the Moon's orbit, courtesy NASA: