What Is a Lunar Eclipse?
A lunar eclipse happens when the Moon moves into Earth’s shadow. It can only happen at a full Moon, when the Sun, Earth and Moon line up closely enough for Earth to block direct sunlight from reaching the Moon. The Moon dims, and during a total lunar eclipse it can turn red or orange.
A lunar eclipse is one of the most visible astronomical events on Earth. Unlike a solar eclipse, which can only be seen from a relatively narrow part of the planet, a lunar eclipse can be seen from much of the half of Earth that is in night.
What is a lunar eclipse?
The Moon makes no light of its own. We see it because it reflects sunlight, which is why it shows phases as the Sun-facing side of the Moon turns toward or away from us.
During a lunar eclipse, Earth gets in the way. It blocks some or all of the direct sunlight that would normally reach the Moon, and the Moon travels through the shadow Earth casts into space. Nothing happens to the Moon itself. It is simply passing through the dark.
The shadow has been a clue to science for a long time. Greek thinkers such as Aristotle pointed out that Earth’s shadow on the Moon always has a curved edge, one of the early arguments that Earth is round.
How does a lunar eclipse happen?
A lunar eclipse needs three bodies lined up in order: the Sun, then Earth, then the Moon. The alignment only has to be close enough for the Moon to touch Earth’s shadow. It does not have to be a perfect straight line for every type of eclipse.
- The Sun lights up Earth and the Moon.
- Earth blocks some of that light and casts a long shadow into space, on the side facing away from the Sun.
- At the right full Moon, the Moon’s orbit carries it through that shadow.
- How deeply the Moon enters the shadow decides which type of eclipse you get.
The Moon orbits Earth from west to east, so it moves through the shadow in that direction. The shadow usually first appears on the Moon’s eastern edge, which is the left-hand side as seen from the Northern Hemisphere, and it leaves from the opposite side.
Why doesn’t a lunar eclipse happen every full Moon?
A lunar eclipse always needs a full Moon, but most full Moons miss Earth’s shadow. The reason is geometry. The Moon’s orbit is tilted by about 5 degrees compared with the plane of Earth’s orbit around the Sun. At most full Moons the Moon passes a little above or below the shadow.
The two points where the Moon’s tilted orbit crosses Earth’s orbital plane are called the nodes. An eclipse can only happen when a full Moon falls close enough to one of them, which in practice means eclipses come in two seasons a year, roughly half a year apart. For a closer look at how the lunar cycle and eclipses fit together, see Moon phases and lunar eclipses.
The three types of lunar eclipse
Lunar eclipses are sorted by how much of the Moon enters Earth’s darkest shadow, the umbra.
| Type | What happens | What you see |
|---|---|---|
| Total | The whole Moon enters the umbra | A darkened Moon, often red or orange |
| Partial | Part of the Moon enters the umbra | A dark shadow covering part of the Moon |
| Penumbral | The Moon passes through only the penumbra | Subtle dimming, often hard to notice |
Total lunar eclipse
The entire Moon moves into the umbra. This is the dramatic one, and the type that can produce the famous red or orange Moon. Every total eclipse also includes partial and penumbral stages before and after totality.
Partial lunar eclipse
Only part of the Moon enters the umbra. The shadow looks like a dark bite taken out of the Moon, and the bite grows and shrinks as the Moon passes through.
Penumbral lunar eclipse
The Moon only passes through Earth’s fainter outer shadow. The dimming is slight, and many people looking at the sky would not notice anything unusual without knowing when to look. The shading tends to be easiest to see near the middle of the eclipse.
What are the umbra and penumbra?
These two words come up constantly in eclipse explanations, and they are simple once you see them side by side.
- Umbra: the dark inner part of Earth’s shadow, where Earth blocks the Sun’s direct light.
- Penumbra: the lighter outer part of the shadow, where Earth blocks only some of the Sun’s light.
At the distance of the Moon, Earth’s umbra is a little over two and a half times as wide as the Moon, which is why the Moon can sit completely inside it during a total eclipse. The stages and timings of an eclipse are defined by when the Moon touches the edges of these two shadows, which our lunar eclipse phases guide covers in detail.
Why does the Moon turn red?
Even during a total lunar eclipse, Earth does not block every bit of sunlight from reaching the Moon. Some sunlight passes through Earth’s atmosphere on its way past the planet. The atmosphere scatters short blue wavelengths far more than long red ones, which is the same reason sunsets look red, so mostly red and orange light is bent around Earth and onto the Moon.
In effect, the Moon is lit by all of the sunrises and sunsets around the edge of Earth at once.
How red it looks varies from one eclipse to the next. Dust, clouds and volcanic material in Earth’s atmosphere can make the Moon look darker or redder. Some eclipses glow bright copper, and others fade to a dim brownish gray.
The reddish Moon is often called a Blood Moon. That is a popular name rather than a technical term. If you are curious about runs of total eclipses, see our article on the lunar tetrad and Blood Moon tetrads.
How long does a lunar eclipse last?
Two different times matter here, and people often mix them up.
- The whole eclipse: from the Moon first touching the penumbra to leaving it. For a total eclipse this can be several hours, up to roughly six.
- Totality: the period when the Moon is entirely inside the umbra. It is much shorter, lasts up to about 1 hour 47 minutes, and varies from eclipse to eclipse depending on how centrally the Moon crosses the shadow.
Partial and penumbral eclipses have no totality, and their length varies a lot. For the exact stages and what to watch for at each one, our lunar eclipse phases guide has the full timeline.
When can you see a lunar eclipse?
A lunar eclipse happens at full Moon, and you can see it from any place where the Moon is above the horizon while the eclipse is under way. That means the night side of Earth, which is roughly half of the planet. A single lunar eclipse can therefore be seen across a huge region, from entire continents at once, though in practice people at the edges may only catch the start or the end.
You do not need any equipment. Binoculars or a telescope add detail, and if you want to photograph the event, see our guide to lunar eclipse photography.
Lunar eclipses in 2027
2027 has three lunar eclipses, and all three are penumbral, so there is no total or partial lunar eclipse that year. Times are in UTC at greatest eclipse, from the eclipse catalog used in our 2027 Lunar Almanac.
| Date (UTC) | Type | Penumbral magnitude | Best seen from |
|---|---|---|---|
| Feb 20, 23:13 | Penumbral | 0.93 | Africa and Europe best placed; also western and southern Asia and the Atlantic side of the Americas |
| Jul 18, 16:03 | Penumbral (extremely shallow) | 0.0014 | Centred on Australia; the Moon shows no noticeable change |
| Aug 17, 07:14 | Penumbral | 0.55 | The Americas and the Pacific, including North America |
Penumbral magnitude is how deeply the Moon enters the faint outer shadow. A value below about 1 means the Moon is not fully inside the penumbra at greatest eclipse.
Is it safe to look at a lunar eclipse?
Yes. It is safe to look at a lunar eclipse directly, with your unaided eyes, binoculars or a telescope. No special eclipse glasses are needed, because you are looking at the Moon, not at the Sun. That is the big practical difference from a solar eclipse.
Lunar eclipse vs. solar eclipse
| Lunar eclipse | Solar eclipse |
|---|---|
| Earth is between the Sun and the Moon | The Moon is between the Sun and Earth |
| Earth’s shadow falls on the Moon | The Moon’s shadow falls on Earth |
| Happens at full Moon | Happens at new Moon |
| Safe to view directly | Needs proper eye protection, except during brief totality under specific conditions |
| Visible across a large area | Totality follows a narrow path |
For eclipses of both kinds, including dates and visibility, head to our eclipses page.
Frequently asked questions
What is a lunar eclipse in simple terms?
A lunar eclipse happens when Earth moves between the Sun and the Moon, causing Earth’s shadow to fall across the Moon.
What causes a lunar eclipse?
A lunar eclipse is caused by the alignment of the Sun, Earth and Moon during a full Moon, allowing the Moon to pass through Earth’s shadow.
Why doesn’t a lunar eclipse happen every full Moon?
The Moon’s orbit is tilted by about 5 degrees relative to Earth’s orbital plane, so most full Moons pass above or below Earth’s shadow.
What are the three types of lunar eclipse?
The three types are total, partial and penumbral lunar eclipses. In a total eclipse the whole Moon enters Earth’s umbra, in a partial eclipse only part of it does, and in a penumbral eclipse the Moon passes only through the fainter outer shadow.
Why does the Moon turn red during a lunar eclipse?
During a total lunar eclipse, some sunlight passes through Earth’s atmosphere before reaching the Moon. The atmosphere scatters more of the blue light, leaving red and orange wavelengths to illuminate the lunar surface.
Is it safe to look at a lunar eclipse?
Yes. Unlike a solar eclipse, a lunar eclipse is safe to view with your unaided eyes, binoculars or a telescope, because you are looking at the Moon and not at the Sun.
Does a lunar eclipse only happen during a full Moon?
Yes. A lunar eclipse can only occur at full Moon, although not every full Moon produces an eclipse.
How long does a lunar eclipse last?
The whole event, from the first touch of the penumbra to the last, can take several hours, up to roughly six for a total eclipse. Totality, when the Moon is fully inside the umbra, lasts up to about 1 hour 47 minutes and is often shorter.
How often do lunar eclipses happen?
A year typically has two or three lunar eclipses, counting penumbral ones, though the number and types vary from year to year. 2027 has three, and all three are penumbral.
What is the difference between the umbra and the penumbra?
The umbra is the dark inner part of Earth’s shadow, where Earth blocks the Sun’s direct light. The penumbra is the lighter outer part, where Earth blocks only some of it.
Can a lunar eclipse be seen from anywhere on Earth?
No. It can be seen from any place on the night side of Earth where the Moon is above the horizon during the eclipse. That is a large share of the planet, so depending on where you live you may see all of it, part of it, or none of it.
What is a Blood Moon?
Blood Moon is a popular name for the reddish Moon seen during a total lunar eclipse. It is not a formal astronomical term.