Lunar Eclipse Explained

A lunar eclipse happens when Earth gets between the sun and the moon, and casts a shadow on the moon. The moon doesn’t go dark, though — it turns a deep coppery red, sometimes orange or brown, depending on the conditions in Earth’s atmosphere.

That’s why lunar eclipses are often called blood moons. They’re free, safe to look at directly, and usually visible for hours. Here’s the explainer.

How a lunar eclipse actually works

Three things have to line up: the sun, Earth, and the moon, in that order. Earth has to be in the middle, with the moon directly behind it from the sun’s point of view.

This lineup only happens at full moon, because that’s the only time the moon is on the opposite side of Earth from the sun. (At new moon, the moon is between us and the sun — which is when solar eclipses happen instead.)

But the moon’s orbit is tilted by about five degrees relative to Earth’s orbit around the sun. So most full moons, the moon passes slightly above or below Earth’s shadow rather than through it. A lunar eclipse only happens when the geometry lines up precisely — roughly two or three times a year.

The 2026 calendar above shows both of this year’s lunar eclipses — the total on March 3 and the partial on August 28 — with an Above horizon / Below horizon flag for your location. Full filterable year at skywhen.com/tools/2026-sky-calendar.

Why the moon turns red

You’d expect a moon in Earth’s shadow to just go dark. But sunlight doesn’t move only in straight lines through space — when it grazes Earth’s atmosphere on its way past, the atmosphere bends and filters it.

Blue light scatters out (which is why our daytime sky is blue, and our sunsets are red — the blue has been scattered away by the longer path through the atmosphere). What’s left over is the red and orange end of the spectrum.

That red and orange light bends around Earth and falls on the moon. So a moon inside Earth’s shadow is, in effect, lit by every sunset and sunrise on Earth at once.

The three types of lunar eclipse

Penumbral

The moon passes through the outer, faint part of Earth’s shadow. The effect is subtle — most people don’t notice. The moon dims slightly but doesn’t change color. Not really worth setting an alarm for.

Partial

Only part of the moon enters the dark inner shadow (the umbra). You see a dark bite taken out of the moon, but the unshadowed portion stays normal-colored. Pretty, but not as striking as a total eclipse.

Total

The entire moon enters the umbra. This is when you get the deep red color. Totality usually lasts somewhere between 30 minutes and an hour and 45 minutes — the longest possible totality is about 1 hour 40 minutes.

The whole eclipse, from first contact with the umbra to the moon leaving it, takes roughly three hours.

How often lunar eclipses happen

On any given year, Earth gets two to four lunar eclipses. (At least two — that’s guaranteed by orbital geometry — and up to five in an unusually busy year.)

A total lunar eclipse happens, on average, every two to three years from any one location on Earth. Unlike solar eclipses, which require you to be in a narrow path, lunar eclipses are visible from the entire night side of Earth at once — anyone in the right hemisphere can see one without traveling.

How to watch one

No equipment needed. No eye protection needed. Step outside, look up.

• Check the times. Local times for first contact, totality start, greatest eclipse, totality end, and last contact are available from any astronomy calendar.
• Skip the city centers if you can. A bright urban sky still lets you see a total lunar eclipse fine, but the surrounding stars look much more striking from a darker spot.
• Binoculars are a nice upgrade.They make the color more vivid and show texture on the moon’s shadowed surface. Not necessary.
• Plan for 2–3 hours. The partial phases on either side of totality are interesting too — the moon visibly walks into and out of the shadow.

The 2026 lunar eclipses

Total — March 3, 2026

Visible across the Pacific, Asia, Australia, and western North America. Totality lasts about 58 minutes. The moon is at average distance for this one (about 382,600 km), so it’s not a supermoon — but the red color during totality is what matters anyway.

Partial — August 28, 2026

About 93% of the moon enters Earth’s umbra at maximum. Visible from the Americas, most of Africa, and Europe. Not a total eclipse, but close enough to feel like one.

The Danjon scale

Lunar eclipses aren’t all the same color. The exact shade depends on how much dust, volcanic ash, and cloud cover is in Earth’s atmosphere at the time. The Danjon scale rates lunar-eclipse darkness from 0 (almost black) to 4 (bright orange-red).

After major volcanic eruptions, the next year or two of eclipses tend to be very dark — sometimes barely visible. After clean-atmosphere years, eclipses can be startlingly bright. Most fall somewhere in the middle.

The bridge: keeping the night

Lunar eclipses are slow events. You stand outside for an hour while the moon gradually changes color. The conditions of the night — who’s with you, where you’re standing, whether you bring a thermos — become part of the memory.

A custom star map of the eclipse night captures the moon’s position in the sky, the phase, and the surrounding stars from your exact location. The moon shows as full (because lunar eclipses always happen at full moon), and the constellation backdrop reflects the true sky from that night. Try the date at the SkyWhen customizer — the preview is free.

For solar-eclipse explainers, see Solar Eclipse Explained. For the “why is it called a blood moon” angle, see Blood Moon Explained.

The night the moon turned red — held still, exactly as it was.

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