Memento Astra: Astrology, and the 36 Decans Behind the Minor Arcana

Memento Astra is the astrology site built alongside this one. Same builder, same house rules, one shared sign-in.

It is worth your attention even if astrology is not your subject, because the answer to a question most readers eventually ask lives over there. That question is why the Three of Cups on a Rider-Waite-Smith style deck carries a planet and a sign at all.

What the site actually is

It computes rather than describes. There are no star sign columns on it.

• A birth chart calculator that takes a date, a time and a place and returns real planetary positions from the Swiss Ephemeris, the same data professional astrology software uses.
• A death chart, which almost nobody else builds: the same reading cast for a recorded date of death. Reflective rather than predictive, and every worked example uses a date of public record.
• Astrocartography, the lines a chart draws across a world map, with the calculation explained rather than asserted.
• Famous birth and death charts, thousands of them, each carrying a Rodden rating so you can judge how good the underlying birth data is.
• Current planets and an ephemeris for anyone who wants the raw positions.

Its house rule is the one you already know from here: it says what something is associated with, never what will happen to you.

The real link between the two sites

The 36 decans.

A decan is a ten degree third of a zodiac sign. Twelve signs, three decans each, 36 in total. They are considerably older than tarot: Egyptian in origin, groups of stars used to mark the hours of the night, later absorbed into Hellenistic astrology and carried through the medieval and Renaissance traditions.

The minor arcana has exactly 36 pip cards, the two through ten of each suit. In the 1880s the Hermetic Order of the Golden Dawn mapped one set onto the other. Arthur Waite and Pamela Colman Smith were both members, which is why the deck almost everybody now learns on carries those attributions.

The rule behind it is tidy:

• Suits follow the elements. Wands fire, Cups water, Swords air, Pentacles earth.
• Ranks follow modality. Within each element the cardinal sign takes two, three and four, the fixed sign takes five, six and seven, and the mutable sign takes eight, nine and ten.

Work it through and the Five of Cups is the first decan of Scorpio, the Eight of Wands is the first decan of Sagittarius, and the whole minor arcana turns out to be a map of the zodiac at ten degree resolution.

Almost nobody learning tarot is told this. It reframes the pips from 36 separate things to memorise into one structure with a shape.

Reading it from both ends

This site's card and astrology pages give every zodiac and planetary attribution from the card side. Astra's decan pages give all 36 from the sky side, including which card each one takes.

Both sites compute those attributions from the rule rather than transcribing a table, and each one's test suite checks its answers against the other's data. If they ever disagree, one is wrong and the build fails. That is a slightly obsessive way to handle a nineteenth century correspondence system, and it is the reason you can trust either page.

Something you can actually do with it

Find the decan your own Sun sits in.

It depends on the exact degree rather than the date range, so it needs a real chart rather than a birthday. Cast one on Astra's calculator, read the degree, and look up the card.

It works for every placement, not just the Sun, which gives you a small handful of cards with a personal connection that is inherited rather than invented. If you would rather come at it from this side, the tarot birth card here works straight from a date of birth, and my tarot year does the same for the current year.

What the two sites share underneath

One account, so the sign-in that holds your reading journal here holds saved charts on Astra.

And the same refusal to overclaim. This site is clear that tarot is a reflective tool rather than a forecast, and Astra is clear that a chart describes associations rather than events. Neither one will tell you what is going to happen, and both would rather be useful than impressive.

Where to start

Cast a chart on Astra. You need a date, a time and a place, and the time matters more than most people expect.

Then read this site's decans and attributions with your own degrees in front of you. That is the order that makes the mapping land.