Lunar Eclipse Calendar

Every lunar eclipse is the Moon passing into the Earth's shadow. That shadow has two parts: a dark inner cone where the Sun is completely blocked, and a faint outer region where it is only partly blocked.

In a total lunar eclipse the Moon passes entirely into the dark inner shadow. It does not disappear — it turns a deep copper red, lit by sunlight bent around the Earth through our atmosphere. Totality typically lasts an hour or more.

In a partial lunar eclipse only part of the Moon enters the dark shadow, giving it a distinct curved bite for an hour or two. The bitten edge is the shadow of the Earth, and its curve is the same observation that told the Greeks the Earth was a sphere.

In a penumbral lunar eclipse the Moon crosses only the faint outer shadow and dims slightly. It is a real eclipse and it is almost impossible to notice: most people looking up would see an ordinary full moon, and photographs taken before and after are the usual way of telling.

This calendar lists penumbral eclipses rather than quietly dropping them, and says which they are. Leaving them out without explanation is how a calendar ends up looking wrong to anyone comparing it against another.

If the Earth's shadow were simply an absence of light, a fully eclipsed Moon would go black. It does not, and the reason is our atmosphere.

Sunlight grazing the edge of the Earth is bent inward by the air, in the same way light bends through a lens, and some of it lands on the Moon. On the way through it loses most of its blue: the same scattering that makes the sky blue overhead and sunsets red on the horizon removes the short wavelengths first.

What reaches the Moon is therefore the light of every sunrise and sunset on Earth at once, and it is red. The nickname blood moon comes from this and describes nothing more sinister than atmospheric physics.

How red varies. A year with major volcanic dust or heavy cloud along the day-night line gives a darker, browner eclipse; a clear atmosphere gives a brighter copper. The colour is a readout of the state of our own air, seen from a quarter of a million miles away.

Not every total lunar eclipse looks the same. Some are a bright coppery orange with a clearly visible disc; others are so dark the Moon nearly vanishes.

Astronomers grade this on the Danjon scale, which runs from L=0 for an eclipse so dark the Moon is almost invisible at mid-totality, through L=2 for the familiar deep red, to L=4 for a bright coppery-orange eclipse with a bluish rim.

What decides it is the state of the Earth's atmosphere along the line between day and night, because that is the air the light passes through. A year with major volcanic dust in the stratosphere gives dark eclipses; the darkest on record followed large eruptions.

It is a genuinely unusual measurement: a number you estimate by eye, describing the clarity of our own atmosphere, read off a rock a quarter of a million miles away. It also cannot be predicted reliably in advance, which makes it one of the few things about an eclipse that is still a surprise.

A solar eclipse is visible from a band a hundred kilometres wide. A lunar eclipse is visible from every place on Earth where the Moon is above the horizon, which is roughly half the planet.

The difference is which body is in shadow. In a solar eclipse the Moon's small shadow falls on the Earth, so only the people inside that shadow see anything. In a lunar eclipse the Earth's much larger shadow falls on the Moon, and the Moon itself is what changes — so anyone who can see the Moon at all sees the same thing at the same moment.

That is also why the times in this calendar need no location. The instant of greatest eclipse is a single moment worldwide; all that changes from place to place is whether the Moon has risen where you are.

And unlike a solar eclipse, a lunar eclipse is completely safe to watch with the naked eye, for as long as you like, with no filter of any kind. There is nothing to protect against: you are looking at a dimly lit rock, not at the Sun.

A lunar eclipse asks less of you than almost any astronomical event. No filter, no equipment, no travel, and no precise timing — the interesting part lasts over an hour rather than minutes.

Find the Moon, check that it is above your horizon at the time in the table, and look. Binoculars deepen the colour noticeably and a telescope is unnecessary. A dark sky helps but is not required: the Moon is bright enough to survive a city.

The partial phase is worth catching from the beginning, because the curved edge of the Earth's shadow creeping across the surface is more striking in motion than the totality that follows. That curve is the oldest evidence for a round Earth, and it is visible from a balcony.

Photography is easy and forgiving. A phone will not capture the colour well, but any camera with manual exposure and a modest zoom will, at exposures long enough that a tripod matters more than the lens.

Astrologically a lunar eclipse is a full moon on the nodal axis, so it is read as a culmination rather than a beginning — something reaching the point where it has to be dealt with.

The degree in the table above is the Moon's position at greatest eclipse, which is always exactly opposite the Sun. As with any eclipse, the degree is public and identical for everyone; whether it lands on something in your own chart is the part that varies.