(Describer) "What is a Lunar Eclipse? Dr. Andrew Layden. Chair, Department of Physics & Astronomy. Bowling Green State University."

[gentle music]

(speaker) A lunar eclipse is when the moon's orbit takes it behind the Earth so that the Earth's shadow is cast out into space and the moon travels into the Earth's shadow. It gets darkened for a short period of time, or eclipsed. We might think that it always passes exactly behind the Earth, so that Earth's shadow is cast out into space and moon would pass into the Earth. But actually, the moon's orbit is tilted a little bit, and so that sometimes, in fact, most months, during a full moon, the moon goes above or below the Earth's shadow, and so we get no eclipse at all.

(Describer) A graphic shows the Moon's orbit.

Rarely, the moon's orbit takes it exactly through the center of the shadow, and that's when we get the rarer total lunar eclipse. It happens during a full moon, so usually you think of a full moon as bright, but suddenly the full moon will dim and often redden as well. A blood moon is a term sometimes used to describe the red color that a total lunar eclipse gets. Sunlight traveling past the Earth interacts with the air around the edges and the red light gets bent in and illuminates the moon, whereas all the blue light gets blocked, causes a dull red or coppery color to the moon during a total lunar eclipse.

(Describer) A red Moon lights a starry sky.

I've seen several lunar eclipses. They're fairly easy to see. They happen a couple times a year, typically. There are some similarities between a total lunar eclipse and a partial lunar eclipse. A total lunar eclipse has to have those partial phases before and after it. A partial lunar eclipse, you only see the cookie bites and you never see a totally dark moon. We have total solar eclipses and we have annular solar eclipses. We have total lunar eclipses. Why don't we have annular lunar eclipses? And the reason has to do with who's eclipsing who. With an annular solar eclipse, what happens is, because the moon is far enough away in its orbit it doesn't completely cover the Sun's bright surface and so you see a ring or annulus of bright solar surface around the dark, dark moon. With a lunar eclipse, We're on the other side of the Earth's orbit. The Earth is casting a shadow out into space and the moon passes through that shadow, and so there's no bright surface of the sun to produce a ring or annulus to make an annular lunar eclipse. Lunar eclipses occur about every two years or so. You can't see a lunar eclipse during the day. Most people miss about half of the lunar eclipses that occur. Accessibility provided by the U.S. Department of Education.

(Describer) Accessibility provided by the US Department of Education.