Birth Chart Basics
A birth chart is a diagram of where the Sun, Moon and planets were, as seen from your exact birthplace, at the exact moment you were born. It is astronomy: the positions are calculated and...
Strip away the symbols and a birth chart is a circle representing the ecliptic, the path the Sun appears to travel through the year, divided into twelve thirty-degree signs. On it are marked the positions of the Sun, Moon and planets at your moment of birth, plus the four angles, which depend on where on Earth you were.
Everything on that diagram can be checked against an ephemeris or against NASA. The positions are not a matter of belief. Whether they describe you is a separate question, and a much larger one.
The planets' positions barely change in a day, so a chart from a date alone gets most of them right. The angles do not work like that. The Earth turns once every twenty-four hours, which drags the entire house system round the chart at about one degree every four minutes and one whole sign every two hours.
That is why two people born the same day in the same city can have charts that look nothing alike, and why a chart calculated without a time is missing the layer that makes it personal.
Signs, houses and aspects. A sign is how something behaves. A house is where in life it happens. An aspect is how two things get along. Every statement in a chart reading is one of those three, or a combination of them, and knowing which is which stops a chart feeling like an undifferentiated pile of symbols.
It is not a horoscope. A horoscope is a short piece of writing about one Sun sign and a current period; a chart is a diagram of one person's sky. It is not a prediction, and it is not your future written down anywhere.
It is also not your star sign. A Sun sign is one out of roughly forty pieces of information in a chart, and reading only it is like describing a book by its title.
| Part | What it is | Needs a birth time? |
|---|---|---|
| Sun sign | Which sign the Sun was in | Only if born within a day of a boundary |
| Moon sign | Which sign the Moon was in | Often, because the Moon can change sign inside a day |
| Planet signs | Where Mercury through Pluto were | Rarely |
| Rising sign | The sign coming over the horizon | Yes, absolutely |
| Houses | The twelve divisions of your life | Yes, all of them |
| Aspects | The angles between planets | Mostly no, except aspects to the angles |
A circle, divided into twelve. Around the outside, the signs. Inside, twelve numbered segments, the houses, starting from the left and running anticlockwise. Scattered on the circle, the glyphs for the planets, each with a degree next to it. Across the middle, lines joining planets that are in aspect.
That is the whole of it. Everything else, the colours, the tables down the side, the little symbols for dignities, is software adding convenience. A chart drawn by hand in 1500 and one printed by an app today carry the same information, and a reader of either would recognise the other.
how to read a birth chart, then the Big Three, then how to find your birth time.
Everything on this page is general by necessity. A reading built from your own date, time and place is the version that names your placements rather than describing the categories they fall into. If you do not know your birth time, this covers how to find it.
A diagram of where the Sun, Moon and planets were, from your birthplace, at your moment of birth.
No. A horoscope is writing about one Sun sign for a period. A chart is a diagram of one person's sky.
Close is enough for most of it. Four minutes moves the houses a degree, so an hour of error can move an entire house boundary.
RubyAstro writes about astrology for reflection and self-understanding. Nothing here is medical, legal or financial advice, and none of it is a prediction of events. Read our full disclaimer.
Finding Your Birth TimeIf you were born in the US between 1945 and 1991, there is a real chance your birth time was recorded under a daylight saving rule your chart calculator does not know about. Here is how to check.
Your Age in AstrologyYour age tells you which house your year belongs to. It takes one piece of arithmetic, it works without software, and it is the fastest way to know what a year is about.
Finding Your Birth TimeMost of your chart does not need the hour. Every planet except the Moon stays in the same sign all day, and so does every aspect between them. Here is exactly what you keep, what you lose, and what to do about the gap.
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