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This year

A year on the ecliptic

The wheel below shows the year as a clock — each cardinal point sits at a quarter turn. Earth's tilt swings the sun's declination between +23.44° (June solstice) and −23.44° (December solstice); the equinoxes are the zero crossings.

The next twelve years

Dates are computed with Jean Meeus's polynomial approximation (Astronomical Algorithms, ch. 27) — accurate within a few minutes for the current century.

A few facts about turns

Axial tilt

23.44° · the obliquity of the ecliptic. This is what gives Earth its seasons.

"Equal day & night"

Equinox literally means equal, but sunrise/sunset are reckoned from the sun's upper limb at the horizon (and refraction). The actual equilux — day = night — falls a few days before March's equinox and after September's.

Northern vs southern

Seasons swap across the equator. The June solstice is summer in the north and winter in the south; September is autumn / spring.

Tropics

The latitudes where the sun is directly overhead at solstice: 23.44° N (Tropic of Cancer) and 23.44° S (Tropic of Capricorn).

Arctic & Antarctic circles

66.56° latitude — the boundary inside which the sun stays above (or below) the horizon for at least 24 h at the solstice.

Why dates drift

Years are 365.2422 days. Leap years correct most of the drift; the cardinal-point dates still wander by ~½ day over a century.