Observation 11

Eclipses

The Moon across the Sun and the Earth's shadow across the Moon: the next total, annular and lunar eclipses, from where you would have to stand to see them.

Working out when this is best placed from where you are…

Latitude

Longitude

Which night

Date

Hour

Used for this lesson only — your map settings, and every other lesson, stay as they are.

Sources

NASA Eclipse Web Site (Espenak) — Solar Eclipses: 2021 to 2030: gamma, the point of greatest eclipse and the central durations this page's eclipses are tested against
NASA Eclipse Web Site (Espenak) — Lunar Eclipses: 2021 to 2030: umbral and penumbral magnitudes and the durations of totality
Espenak & Meeus, Five Millennium Canon of Lunar Eclipses, NASA/TP-2009-214172 — Danjon's rule for the size of the Earth's shadow
Meeus, Astronomical Algorithms, 2nd ed. (1998), ch. 25 and 47 — the Sun's and the Moon's positions and distances
NASA Science: Eclipse safety — solar viewers for every partial phase, and the naked eye only in totality
NASA Moon Fact Sheet — the Moon's 1737.4 km radius and its 356,400 to 406,700 km range of distance

← GUIDES

The next total eclipse of the Sun, from the middle of its path: the readout says when and where. An hour before totality the Moon has taken a bite from the Sun's western edge. Never look at a partly covered Sun without eclipse glasses — even a sliver burns.

Now run the last hour. The Moon moves east over the Sun by about its own width an hour. Watch the readout as well as the sky: with nine tenths of the Sun covered it is still day, because a tenth of the Sun is a lot of light. Only in the last minutes does the light fail.

Totality. The Moon covers the whole face of the Sun, and what its glare always hid comes out: the corona, the Sun's outer atmosphere, a million times fainter than the face. For these few minutes, and only these, it is safe to look without a filter.

Pull back. Midday has become a deep twilight, and the brightest planets and stars are out. You are standing in the Moon's shadow: a patch at most a few hundred kilometres wide, racing east faster than an airliner. Outside it the sky is still lit, so the whole horizon glows like a sunset.

The next annular eclipse. The Sun is 400 times wider than the Moon and about 400 times farther away, so the two look the same size. But the Moon's orbit is an ellipse, and near its farthest it looks about 12% smaller than at its nearest: too small to cover the Sun, it leaves a ring of fire.

The next total eclipse of the Moon. Now the Earth is between the Sun and the Moon, and a full Moon is moving into our shadow. Its edge is curved, at every eclipse and at every angle — the evidence Aristotle gave that the Earth is a sphere. Anyone on the night side can watch, with no filter at all.

Run the hour into totality. The Moon moves east into the umbra, the shadow's dark core, a little over its own width an hour. The part outside still shines white; the part inside turns not black but a dim copper red.

Totality. The Moon glows red because the Earth's air bends sunlight into the shadow and takes the blue out first: it is lit by every sunrise and sunset on Earth at once. And with the full Moon's glare gone, the faint stars come back around it.

Why not every month? The fine dashed line is the Moon's path, tilted 5° to the ecliptic, the Sun's. They cross at two nodes, and tonight's full Moon is at one — the Sun, opposite, at the other. Eclipse Seasons follows that through the year.