Solar Eclipse Calendar

Every solar eclipse is the Moon passing between the Earth and the Sun. What varies is whether the Moon looks big enough to cover the Sun, and whether the shadow axis actually reaches us.

In a total solar eclipse the Moon covers the disc completely. The sky darkens to something like deep twilight, the corona becomes visible, the temperature drops and bright stars appear. It lasts minutes, and only inside a band roughly a hundred kilometres wide.

In an annular solar eclipse the alignment is just as good but the Moon is further from Earth and looks slightly too small. A ring of sunlight is left around it. The sky does not darken, the corona never appears, and there is no moment when it is safe to look without a filter.

In a partial solar eclipse the shadow axis misses the Earth entirely and only the outer shadow touches us. The Sun looks bitten into. This is what most of the world sees during any solar eclipse, including the ones that are total somewhere else.

The difference between total and annular is a few per cent of apparent diameter — the Moon's distance from Earth varies by about ten per cent over a month, and that is enough to decide which of the two you get.

There are two or three solar eclipses in a typical year, which does not sound rare at all. What is rare is standing in the right place.

The Moon's shadow is small. Where it touches the Earth it makes a spot at most a couple of hundred kilometres across, and that spot sweeps a track a few thousand kilometres long before the geometry runs out. A track that size covers a tiny fraction of the surface, and most of it is ocean.

The result is that any given place sees a total solar eclipse roughly once every three or four hundred years on average, while the Earth as a whole gets one every eighteen months. The scarcity is a fact about you, not about the phenomenon.

That asymmetry is also why partial eclipses feel so much more common. You do not have to be under the shadow axis to see one, only somewhere on the daylit side within reach of the outer shadow, and that is a large piece of the planet each time.

The track of a total eclipse is drawn on maps as a smooth band, which makes it look like a road. It is closer to the mark left by a spotlight swept across a globe.

The shadow spot moves at over a thousand miles an hour near the middle of a track and much faster near its ends, where it strikes the Earth at a shallow angle and stretches. That is why totality lasts longest near the middle of the path and why the band widens and thins along the way.

It is also why so many tracks land on water. Oceans cover most of the surface, and the shadow does not care: a great many total eclipses are seen properly only by people who put themselves on a ship or a plane, and a few are seen by nobody at all.

Distance from the centre line matters more than distance along it. Fifty kilometres to the side costs a large fraction of the totality; a thousand kilometres further along the same line costs almost nothing. Anyone travelling aims at the line, not at the shaded band.

The partial phases take about an hour and are, frankly, undramatic. You need a filter to see anything at all, and the light does not obviously change until the Sun is more than three quarters covered.

In the last minute the change becomes very fast. Shadows sharpen, because the light source is shrinking towards a line. Colours flatten. If the ground is pale you may see shadow bands — faint rippling stripes cast by turbulence high in the atmosphere, visible for only a few seconds and still not fully explained.

Then the last of the photosphere breaks into beads of light along the Moon's edge, shining through valleys on its limb. The final bead alongside the emerging corona is the diamond ring. That is the moment the filters come off, and not a second before.

Totality itself does not look like the photographs. The corona is fainter and more structured than long exposures suggest, stars come out, the horizon glows in every direction at once because you are looking at daylight beyond the shadow, and animals go quiet. Then the diamond ring appears on the other side, and the filters go straight back on.

The whole sequence, first contact to last, runs two to three hours. The part everybody travels for is the few minutes in the middle.

Astrologically a solar eclipse is a new moon on the nodal axis, so it is read as a beginning with the volume turned up. The degree is the same for everyone; whether it touches your chart is not.

The table above gives the degree of every solar eclipse in the span. Anything within a few degrees of one of your placements — or opposite it, or square to it — is a contact worth knowing about. Everything else is a spectacular astronomical event you can watch without it meaning anything in particular for you.