Big Three Calculator

What the Big Three Are

Astrologers read the Sun, the Moon and the Ascendant first because together they sketch the whole person. The Sun sign describes your sense of purpose and the self you grow into. The Moon sign describes emotional needs, instinct and what makes you feel safe. The rising sign, or Ascendant, describes your manner, the way you begin things and the impression you make before anyone knows you well.

The three often pull in different directions. A Leo Sun with a Cancer Moon and Virgo rising might want to be seen, need to feel protected and come across as careful and modest. Reading them together is where a chart starts to sound like a person.

How the Big Three Are Calculated

The Sun's sign comes from the date: it moves about one degree a day and spends roughly a month in each sign. The Moon moves about 13 degrees a day and changes sign every two to two and a half days, so its sign depends on the date and often on the hour. The rising sign is the zodiac sign on the eastern horizon at the moment and place of birth. It changes about every two hours, so it needs your birth time and birthplace.

If You Don't Know Your Birth Time

You can still find your Sun sign and, on most days, your Moon sign. Tick that you don't know the time and the calculator checks every hour of your birth date, then tells you whether the Moon could have been in one sign or two. The rising sign cannot be found without a time. A birth certificate, a hospital record or a baby book is the best source; failing that, astrologers use birth time rectification.

How Accurate Is It?

Positions come from Selfgazer's astrology engine, the same one that draws the chart in your astro room: VSOP87 planetary theory through Astronomy Engine, with Chiron from Swiss Ephemeris tables. Tested against the Swiss Ephemeris, planets agree to within half an arcminute and house cusps to within a tenth of an arcminute. Your local birth time is converted with your birthplace's historical time zone rules, including past daylight saving changes. Everything is calculated in your browser, and nothing you enter is stored.