What Is A Lunar Eclipse?
QUICK ANSWER
A lunar eclipse happens when Earth passes directly between the Sun and the Moon, casting its shadow on the lunar surface. There are three types: total, partial, and penumbral. Lunar eclipses only occur during full moons and are visible from the entire night side of Earth.
A lunar eclipse is one of the easiest astronomical events to observe. Unlike solar eclipses, which are visible only along narrow paths and require eye protection, lunar eclipses can be seen from anywhere on the night side of Earth and are perfectly safe to watch with the naked eye. Most people will see many lunar eclipses in their lifetime.
What causes a lunar eclipse?
Earth's shadow falling on the Moon. According to NASA, a lunar eclipse occurs when Earth lines up directly between the Sun and the Moon, blocking sunlight from reaching the lunar surface. This can only happen when the Moon is on the opposite side of Earth from the Sun, which means at the full moon phase. Earth casts two shadows: the dark inner umbra (where the Sun is fully blocked) and the lighter outer penumbra (where the Sun is partially blocked). The Moon's position in these shadows determines what type of eclipse occurs.
What are the three types?
Total, partial, and penumbral. A total lunar eclipse happens when the entire Moon passes through Earth's umbra. The Moon often turns reddish during totality (a blood moon). A partial lunar eclipse occurs when only part of the Moon enters the umbra, leaving the rest in the penumbra or normal sunlight. A penumbral lunar eclipse happens when the Moon passes only through Earth's penumbra; this produces only a subtle dimming, often hard to notice without careful observation. Total eclipses are the most dramatic.
Why don't they happen every month?
The Moon's orbit is tilted. The Moon orbits Earth at about a 5-degree tilt to Earth's orbit around the Sun. So during most full moons, the Moon passes above or below Earth's shadow rather than through it. Lunar eclipses only happen when the alignment is precise enough that the Moon actually enters Earth's shadow. The geometry works out to about 2 to 5 lunar eclipses per year somewhere on Earth, with about 1 to 2 being total. The Moon also has to be near a node where its orbit crosses Earth's orbital plane.
How do you watch one?
With the naked eye. Unlike solar eclipses, lunar eclipses are completely safe to view without any eye protection. The Moon's surface during an eclipse is illuminated only by faint reddened sunlight refracted through Earth's atmosphere, far too dim to harm eyes. Binoculars or a small telescope can enhance the view but aren't necessary. A total lunar eclipse can last several hours from start to finish, with totality typically lasting up to about 100 minutes, far longer than total solar eclipses.
A lunar eclipse happens when Earth passes directly between the Sun and the Moon, casting its shadow on the lunar surface. There are three types: total, partial, and penumbral. Lunar eclipses only occur during full moons and are visible from anywhere on the night side of Earth. They're completely safe to view with the naked eye and last much longer than total solar eclipses. About 2 to 5 lunar eclipses happen each year somewhere on Earth.
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