What is a lunar eclipse?
A lunar eclipse happens when the moon passes through some or all of the Earth's shadow. In order for that to happen, the sun, Earth, and moon need to be lined up with the Earth plopping a squat between the other two. Because of this formation, a lunar eclipse can only occur when the moon is full.
There are three types of a lunar eclipse, the rarest of which is the total lunar eclipse. When the moon isn't completely enveloped by the Earth's shadow, you've got a partial eclipse. The moon will look like an apple that's had a bite taken out of it. A penumbral eclipse happens when the trio of spheres are imperfectly aligned. The Earth blocks some of the sun's light from getting to the moon and covers all or part of the moon with the outer part of the planet's shadow, which is called the penumbra. That outer shadow is fainter than the dark center of the Earth's shadow. A penumbral eclipse can look similar to a normal full moon and isn't quite as exciting as the other two types.
Despite being nestled entirely in the shadow of our planet, some sunlight will still reach the moon during a total lunar eclipse. Sunlight passes through the Earth's atmosphere, filtering out blue light. When the sunlight makes its way around the Earth to the surface of the moon, it turns the lunar surface a coppery red color, according to NASA.
The entirety of an eclipse lasts for a few hours, though the total eclipse is only a part of that time span. According to NASA, there are at least two partial lunar eclipses every year. A total lunar eclipse is rarer.