Aries First Decan: March 21 to March 30

The dates

The Sun covers about a degree a day, so a decan takes roughly ten days. These are the calendar dates the Sun spends in the first decan of Aries, computed across 1930 to 2035.

The first and last days shift a little between years, because the Earth's year is 365.2422 days rather than 365 and the whole zodiac drifts about six hours a year against the calendar. March 21 and March 30 are the edges, and both have their own page with the exact figures.

What a decan is, and where the idea came from

A decan is a third of a sign: ten degrees out of thirty, which the Sun crosses in about ten days. Twelve signs give thirty-six of them, and each one carries its own planetary ruler on top of the sign's. That makes a decan roughly three times more specific than a Sun sign while still needing nothing but a birth date.

The idea is older than the zodiac it now divides. The Egyptians used thirty-six groups of stars, each rising about forty minutes after the last, to tell the time at night. Ten of them were visible across a night, which is one of the threads that led to the day being divided into twenty-four hours rather than some rounder number. The decans were on coffin lids and temple ceilings a long time before anybody attached planets to them.

The planetary rulers came later, from Hellenistic astrology, and they run in what is called the Chaldean order: Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon, which is the planets ranked by apparent speed from slowest to fastest. Starting at the first ten degrees of Aries and counting that sequence forward one decan at a time gives every decan its ruler, and it comes out the same every time because it is arithmetic rather than opinion.

Aries through Mars

Aries is Fire and Cardinal, ruled by Mars, and the traits usually attached to it are direct, competitive, quick to start, impatient and brave. Every Aries has that. What the first decan adds is Mars, and the result is a Aries who runs sharper and less patient.

This one is a special case: Mars rules both the sign and the decan, so nothing is being blended. It is Aries at full strength, undiluted, which is the usual reading of a decan ruled by its own sign's ruler. If the sign's reputation ever fits somebody exactly, it tends to be somebody born here.

That table is the argument for decans in one block. Three people can all be Aries and be running it through Mars, Sun and Venus, which is a genuine difference and one a Sun sign on its own throws away.

The tarot card for this decan

The standard English tarot deck was built on this same system. Every pip card from Two to Ten corresponds to one decan, which means the first decan of Aries and the Two of Wands are two descriptions of one ten-degree stretch of sky.

That correspondence is not decoration and it is not something the tarot borrowed loosely. The Rider deck of 1909 was drawn to a scheme in which the thirty-six pips map onto the thirty-six decans in order, and the card's traditional meaning was derived from the decan's ruler and sign rather than the other way round. Reading the card is another way of reading these ten degrees, and it is frequently the more vivid one.

Mars in Aries is the third description of the same thing, this time as a birth chart placement.

If your birthday falls here

Your Sun is in this decan, which narrows it from one sign in twelve to one stretch in thirty-six. Worth doing something with: read the Mars pages as well as the Aries ones, because half of what is usually described as your sign is being coloured by a planet most descriptions never mention.

The full account of the Sun in Aries is here, and Aries season covers the whole stretch of the year.

If you want the other nine tenths

A decan is the Sun, more precisely. The Moon, the rising sign and the houses all need a birth time, and they are where most of what people actually recognise about themselves lives. If you do not know your birth time, this covers how to find it.