In contrast, during a total solar eclipse — which is preceded by a partial eclipse — the moon completely covers the sun, revealing the sun's outer atmosphere, called the corona, during totality. That's the only time it's safe to look at a solar eclipse with the naked eye, since all of the sun's light is blocked.

As the countdown to the year's first total lunar eclipse begins, here's what to know about the difference between a lunar eclipse and a solar eclipse.