Big Three Calculator
Your Sun, Moon and Rising signs, to the degree, from the real sky at the minute and place you were born.
Ask an astrologer who you are and they will usually start with three placements: the Sun, the Moon and the Rising sign. Together they are called the Big Three. The Sun describes your core identity and what you are growing into. The Moon describes your emotional needs, what comforts you when the day goes wrong. The Rising sign, or Ascendant, describes how you meet the world and how people read you before they know you.
The three move at very different speeds. The Sun spends about a month in each sign, so the date alone almost always settles it. The Moon changes sign every two and a half days, so on some birthdays it matters whether you arrived in the morning or at night. The Ascendant turns through the whole zodiac every day, which is why it needs your birth time and your birthplace.
How it’s calculated
Your birthplace is looked up to find its latitude, longitude and time zone. The time zone’s own history, including whether daylight saving time applied on your birth date, converts your local clock time into Universal Time. From that instant the Sun and Moon are computed as they appeared from Earth, with light-time and aberration included, using the same astronomical models as professional software. Positions computed to within seconds of arc of NASA JPL Horizons.
The Ascendant is the degree of the zodiac rising on the eastern horizon at your birthplace. It is worked out from the apparent sidereal time at your location and the true tilt of Earth’s axis on that date. Signs are tropical, the zodiac of Western astrology, measured from the March equinox. Your full reading divides the chart into Equal houses of 30° each, starting from this Ascendant, so the Rising degree shown here also sets every house in your chart.
If you don’t know your birth time
Leave the time blank and the calculator checks the whole day. You will still get your Sun sign, and your Moon sign too unless the Moon changed sign that day, in which case you will see both and the time it crossed. Your Rising sign has to wait for a time. Birth certificates, hospital records, baby books and older relatives are the usual places to find one.
Frequently asked
What is the Big Three in astrology?
The Big Three are the Sun sign, the Moon sign and the Rising sign (Ascendant) of your birth chart. The Sun stands for your core identity, the Moon for your emotional needs and instincts, and the Rising sign for your outward style and first impressions. Most astrologers read these three together before anything else.
Why do I need my birth time for my Rising sign?
The Rising sign is the part of the zodiac coming up over the eastern horizon when you were born. Because Earth turns once a day, all twelve signs rise in turn, and each one takes roughly two hours to pass (some faster, some slower, depending on the sign and your latitude). A difference of 15 minutes can change the Rising sign when the Ascendant sits near the edge of a sign, so the calculator tells you when that is the case.
I don’t know my birth time. What can I still find out?
Your Sun sign, almost always, and usually your Moon sign. Leave the time blank and the calculator checks the full day of your birth. If the Moon or the Sun changed sign during that day it shows both options and the local time of the change, so you know exactly what an approximate time would settle.
What does it mean to be born on a cusp?
A cusp is the boundary between two signs. If your Sun was within half a degree of that line, the calculator tells you. Astronomically there is no blended sign: at any given minute the Sun is on one side of the boundary or the other, and with a birth time and place we can say which. Many astrologers still read a trace of the neighbouring sign in a cusp Sun.
Why does another site give me a different Moon or Rising sign?
The usual causes are time zones and daylight saving time applied wrongly for historical dates, a birthplace resolved to the wrong town, or a rounded birth time. Some sites also use the sidereal zodiac of Vedic astrology, which sits about 24 degrees away from the tropical zodiac used here. This calculator shows the place, local time and time zone it used, so you can check each step.
Is it free, and what happens to my data?
It is free and needs no sign-up. The birthplace you choose is sent to our server only to look up its coordinates and time zone. The chart itself, including your date and time of birth, is computed in your browser.
Three signs are the start of the story
Arcana Origin computes your whole chart from the same exact ephemeris, planets and Equal houses included, and reads it alongside dozens of other traditions from a single birth date.
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