The Sky in 2030

The moon's phases, the sun's turning points and the festivals kept against them. All of it worked out from the orbital mechanics rather than copied from an almanac, and all of it answerable from the shelves downstairs.

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A birthday, an anniversary, the day something happened: where the sun and moon actually stood, named by six traditions. It runs in your browser and the date is never sent anywhere.

The moon

Each phase is an instant, not a day: the moon is full at a particular minute and the times below are Universal Time. Local time may put one on the day before or after.

The turning points

The equinoxes are the two moments the sun stands on the celestial equator; the solstices are where it reaches its furthest north and south and turns back. The names are northern. South of the equator the June solstice is midwinter, and the whole wheel below turns the other way round.

The eight sabbats

Four of these are the turning points above and move with them, so they are computed. The other four are the cross-quarter days, and those are calendar dates the tradition fixed to the first of a month rather than to the true midpoint of a season. They are printed as the tradition keeps them. Which of the eight are genuinely old, and which were assembled in the twentieth century, is a question the books below do not agree on.

The sun's signs

These are the tropical signs: twelve equal divisions of thirty degrees measured from the March equinox, which is what Western astrology means by a sign. They no longer line up with the constellations they are named after. The equinox has slipped backwards along the ecliptic by about one degree every seventy-two years since the names were given, so the sun now enters the sign Aries while standing among the stars of Pisces. That drift is the precession of the equinoxes, and the library holds books on both sides of the argument about what it means.

Meteor showers

Peaks shift by a day either way with the leap-year cycle, and the rates are the usual maxima under a dark sky with the radiant high — most nights deliver a fraction of them. A shower near a full moon is largely washed out, which the table above will tell you.

Older festivals

Not astronomy, and not dated here as though it were. These are festivals the library's own volumes describe, placed where those volumes place them.

How this page was made. The phases come from the lunar series of Meeus, Astronomical Algorithms, chapter 49; the turning points from chapter 27; the sun's position from chapter 25 and the moon's from a truncation of chapter 47. Two independent routes to the same instants are computed and compared against each other over two centuries and nine thousand phases — a full moon by the first method must read as fully lit by the second, and the largest disagreement is five ten-thousandths of the disc. The check is tools/astro_test.js and it runs before the site is built. The books under each heading were not chosen; the corpus was counted, and these use the term most.

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