Somewhere, at the moment you took your first breath, the sky was doing something specific. The Sun was in one sign, the Moon in another, Mars was off on its own errand, and the eastern horizon was rising through a particular degree of the zodiac. Nobody asked your opinion. A birth chart is simply a photograph of that sky, taken from the exact spot where you were born, and kept.

That is all it is, and that is a great deal. It is not a forecast, it does not change, and it is not a grade. It is the map that every other technique in astrology is read against. A forecast describes what the sky is doing to your chart today. A compatibility reading sets your chart beside someone else's. A planetary return casts a fresh chart at the moment a planet comes home. All of them need the original first, the way a weather report needs a place to be about.

What goes into it

Three things, and all three matter more than people expect.

The date fixes where the planets were. For the slow planets, Jupiter out to Pluto, the date is nearly the whole story: Pluto spends more than a decade in a sign, so everyone in your school year shares it, which is why astrologers read it as a generation more than a person.

The time fixes the houses and the angles. The Ascendant, the degree rising on the eastern horizon, moves about one degree every four minutes. An hour of error moves it fifteen degrees, which is often enough to change your rising sign entirely, and with it the house every planet sits in.

The place fixes the horizon itself. The same moment seen from Lisbon and from Tokyo gives the same planets in the same signs, but a completely different arrangement of houses.

Here is an example that convinces most skeptics in the family. Take twins born twenty minutes apart. Their Sun, Moon and planets are practically identical. Their Ascendant, though, has moved about five degrees, and if it was sitting near the end of a sign, one twin can have Virgo rising and the other Libra. Same parents, same birthday cake, and still one of them labels the spice rack while the other is apologizing to it for the mess.

The four ingredients of a chart

Every birth chart is built from four things, and once you can tell them apart the wheel stops looking like a circuit diagram.

Planets are the actors: the Sun is your sense of self, the Moon your emotional needs, Mercury how you think, Venus what you value and love, Mars how you go after things, and so on out to the outer planets and the lunar nodes. Each is a different drive, and none of them is optional equipment.

Signs describe how each planet behaves. Mars in Aries goes straight at the problem. Mars in Libra goes at it too, but first it checks whether everybody is comfortable with the plan.

Houses describe where it happens: the area of life each planet works in. Venus in the tenth house brings love and charm to the career. Venus in the sixth brings them to the daily routine, and possibly to an unreasonable affection for a well-organized calendar.

Aspects are the angles between planets, and they are where a chart stops being a list and starts being a description of a person. Planets in aspect talk to each other. They cooperate, argue, or lend each other something. The closer an aspect is to exact, the louder the conversation.

A full reading is the combination of all four. "Moon in Cancer" is a sentence. "Moon in Cancer in the tenth house, square Saturn" is a person: somebody who cares deeply, does it in public, and has a strict inner voice asking whether caring this much is professional.

Not every placement weighs the same

This is the part most calculators leave out. A chart is not twelve equal facts. A planet sitting on an angle (the Ascendant, the Midheaven, the Descendant or the bottom of the chart) carries more weight than one sitting quietly in the middle of a house. So does a planet that several others aspect, or the planet that rules your rising sign.

That is why two people with the same Sun sign can feel nothing alike. Imagine two Leos. The first has the Sun conjunct the Ascendant: the Leo is the first thing anyone meets, warm, visible, slightly theatrical about ordering coffee. The second has the Sun tucked away in the twelfth house and Saturn on the Ascendant: the same Leo heart, but behind a reserved, careful front that people mistake for shyness until the karaoke starts. Our birth chart report sorts the placements by weight for exactly this reason, so you read the loud parts first.

A real chart shows the same thing. Albert Einstein was a Pisces, with the Moon in Sagittarius and Cancer rising, and an article about him on this site starts from the Sun. But anyone who knew only "Pisces" would have imagined a dreamier, less stubborn man. Mercury, Venus and Saturn in Aries in his tenth house, the part of the wheel about vocation and public life, with Mercury close to Saturn, are where the stubbornness, the speed and the appetite for picking a fight with Newton come from. The Sun sign is the title of the book, not the plot.

What if you do not know your birth time?

You can still cast the chart, and it is still worth having. The planets will be correct to within a fraction of a degree, except the Moon, which moves about half a degree an hour, so its sign is safe unless it changed sign on your birthday. What you lose is the Ascendant, the Midheaven and the houses. The honest thing to do is read the signs and the aspects, and treat the houses as missing rather than approximate. A guessed house is worse than no house, because it is wrong with confidence.

If you can get the time, get it. Birth certificates in many countries include it, hospitals keep records, and mothers remember a surprising amount, especially if the delivery was long.

A description, not a verdict

A chart does not say what will happen to you or what you must become. A hard aspect names something that will keep asking for your attention, not a sentence passed on you. An easy aspect names something that comes so cheaply it is easy to waste. Every chart has both, including the charts of people you admire, and people who claim theirs has none have not looked closely enough.

What a chart is genuinely good for is recognition: seeing a pattern you half knew about and finally being able to name it precisely. That is usually where it becomes useful, and occasionally where it becomes funny.

When you are ready, cast your birth chart here, then follow it where your questions go: the planets one by one, the aspects between them, or a second chart beside yours.

Frequently asked questions

What is a birth chart?
A map of the sky from your birthplace at the moment you were born: the planets by sign and degree, the houses drawn from the local horizon, and the aspects between everything. It does not change, and it is what every other technique is read against.

Do I need my exact birth time?
For the planets, no: the date is usually enough. For the Ascendant, the Midheaven and the houses, yes. The Ascendant moves a degree every four minutes, so an hour of error moves it fifteen degrees and can change your rising sign completely.

What can I read without a birth time?
Every planet's sign and degree, and every aspect between them, which is most of the chart. Only the Moon is fast enough for the hour to matter, and then only if it changed sign that day. Leave the houses out rather than guessing them.

Which house system do you use?
Whichever you set in your profile, Placidus by default, as most Western astrologers use. The planets are identical in every system; only the house each one falls into can differ, and near a cusp it often does.

What does "sorted by importance" mean?
That the report weighs the placements rather than listing them flat. A planet on an angle, one that several others aspect, or the ruler of your rising sign carries more weight than one sitting quietly mid-house, and reading in that order is the quickest way to see what a chart is mostly about.

Is my birth chart good or bad?
Neither, and anyone who tells you otherwise is selling something. A hard aspect describes something that will keep asking for attention; an easy one describes something that comes cheaply enough to be taken for granted. Both are information, not a sentence.