Lunar eclipse

A lunar eclipse, often called a blood moon, happens when the Moon travels through Earth's shadow. This event takes place during eclipse season, a time when the Moon's orbital path aligns roughly with Earth and the Sun. How long the eclipse lasts and what type it is depends on how close the Moon is to a lunar node. Unlike solar eclipses, which are brief and hard to see, lunar eclipses are visible from any location on Earth that is experiencing nighttime, and they typically last an hour or more. No eye protection is needed to watch them safely.

During a lunar eclipse, the Moon takes on an orange or red color. This happens because, when the Moon moves into Earth's umbra (the dark, central part of the shadow), any sunlight that reaches it must first pass through Earth's atmosphere. Rayleigh scattering then removes shorter wavelengths like blue and violet from that light before it bounces off the Moon and reaches our eyes.

There are several types of lunar eclipses. In a penumbral lunar eclipse, Earth's silhouette only partly blocks the Sun as seen from the Moon, so some direct sunlight still gets through. The Moon sits partially inside the penumbra—the outer, fuzzier part of a shadow cast by a light source that isn't perfectly focused. If the Moon lies entirely within the penumbra, it is called a total penumbral eclipse. From Earth, these events look like a subtle dimming of the Moon's surface. About one-third of all lunar eclipses are penumbral, and only 3% of those are total penumbral.

A partial lunar eclipse occurs when the Moon is partly inside the umbra, where Earth appears large enough in the lunar sky to block the Sun completely. The dark region covered by the umbra looks much more distinct than the dimming of a penumbral eclipse. The Moon's average orbital speed is about 1 kilometer per second, or a little more than its own diameter per hour, so totality can last up to nearly 107 minutes. However, the total time from the first to last contact of the Moon's edge with Earth's shadow can stretch to 236 minutes.

In a total lunar eclipse, the Moon's near side fully enters Earth's umbral shadow. Just before it does, the bright curved edge of the Moon still hit by direct sunlight makes the rest appear dim. Once the Moon is completely inside the shadow, its entire surface becomes more uniformly bright, even revealing stars around it. Later, as sunlight hits the opposite edge, the disk darkens again. This brightness difference occurs because, from Earth, the Moon's limb (its curved edge) reflects more light than the center, due to surface irregularities—similar to how velvet fabric looks darkest at the center of a curve. This effect applies to any airless, cratered body like Mercury when seen opposite the Sun.

The Moon does not go completely black during a total eclipse because Earth's atmosphere bends sunlight into the shadow cone. Without an atmosphere, the Moon would be fully dark. The reddish hue comes from sunlight passing through a long, dense layer of Earth's atmosphere, where shorter wavelengths are scattered away by air molecules and particles. By the time the light reaches the Moon, only longer wavelengths like red remain—the same effect that colors sunsets and sunrises. From the Moon's perspective, the Sun would appear to be setting or rising behind Earth. The amount of refracted light depends on dust or clouds in the atmosphere; more dust removes more non-red light, making the Moon appear a deeper red. Volcanoes, which inject large amounts of dust into the air, can strongly influence the color of a lunar eclipse if an eruption occurs shortly before.

A central lunar eclipse happens when, during a total eclipse, the Moon passes near or through the very center of Earth's shadow, touching the antisolar point. This type is more common.