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Ascendant Calculator

Your Ascendant is the sign of the zodiac that was rising on the eastern horizon at the moment you were born. The calculator finds it the way the UmbraLux app does, from your birth time, your birthplace and the time zone of that day, to the arcminute.

Date of birth

As exact as you can, ideally from your birth certificate.

Your place is missing? Take the nearest town; a few kilometres hardly change the result.

The calculation runs in your browser. Your birth data is neither sent nor stored; only this device remembers your last entry. · Place data: GeoNames (CC BY 4.0)

How the Ascendant is calculated

The calculator runs the same calculation as the UmbraLux app, in four steps:

  1. 1

    Turn the clock time into Universal Time

    Your birth time is the clock time at your birthplace. With the time zone that applied there on that day (the IANA time zone database knows summer times and older rules), it becomes Universal Time (UTC).

  2. 2

    Find the sidereal time at the birthplace

    Universal Time gives the apparent sidereal time at Greenwich. Adding the longitude (15° per hour) gives the sidereal time at the birthplace; as an angle it is the right ascension of the Midheaven (RAMC).

  3. 3

    Intersect horizon and ecliptic

    With the obliquity of the ecliptic ε (about 23.44°) and the latitude φ, the Ascendant's ecliptic longitude is AC = atan2(cos RAMC, −(sin RAMC · cos ε + tan φ · sin ε)).

  4. 4

    Read the sign

    The longitude divided by 30° gives the sign: 0° to 30° is Aries, 30° to 60° Taurus and so on (tropical zodiac). The remainder is the degree within the sign.

Example: 15 May 1990, 14:30, Berlin

Berlin lies at 52.52° north and 13.41° east. On 15 May 1990 summer time applied there (UTC+2), so 14:30 was 12:30 Universal Time.

The sidereal time at the birthplace was 4:55, which makes the RAMC 73.89°; the obliquity of the ecliptic was 23.44°.

That puts the Ascendant at 18°47′ Virgo and the Midheaven (MC) at 15°09′ Gemini. An hour earlier, at 13:30, the Ascendant stood at 8°21′ Virgo: within that hour it rose by about ten degrees.

What the Ascendant means in astrology

Astrology reads the Ascendant as the way you meet the world: your first impression, how you start something new, what others notice first. The Sun sign describes your core, the Moon sign your feelings; together with the Ascendant they are often called the big three of a chart.

In the chart the Ascendant opens the first house, and the sign that rules it is called the ruler of the chart.

Why birthplace and time zone matter

The sky turns once a day above every place, and the Ascendant with it. Your longitude shifts the sidereal time, your latitude decides how fast each sign rises. A calculator that ignores the place or the summer time of the day can be an hour off, which moves the Ascendant by up to a whole sign.

In the library

Questions about the Ascendant

Can I calculate my Ascendant without a birth time?

Not to one sign. In the course of a day all twelve signs rise, at the latitude of Berlin Aries or Pisces in about 50 minutes, Leo to Scorpio in almost three hours. Without a time the calculator shows which sign rose at which time of your birthday; if you know roughly when you were born, you can read it from there.

How exact does my birth time have to be?

On average the Ascendant moves about one degree in four minutes. If it lies in the middle of a sign, a quarter of an hour does not change the sign; near 0° or 29° a few minutes can. The birth certificate is the most reliable source.

Why does another calculator show a different sign?

Mostly because of the time zone or the place: some calculators take no summer time into account, or calculate for Greenwich instead of your birthplace. Vedic astrology uses the sidereal zodiac, whose signs lie about 24 degrees further back at present. And close to a sign boundary, minutes of birth time decide.

Does the calculator use the tropical or the sidereal zodiac?

The tropical zodiac, as Western astrology and the UmbraLux app do: 0° Aries is the vernal equinox.

How accurate is the calculator?

It calculates with the ephemeris Astronomy Engine. In 3,000 test charts, the Ascendant differed from the Swiss Ephemeris, which many astrology programs use, by at most 47 arcseconds. The largest uncertainty is almost always the birth time itself.

Is my data stored?

No. The calculation runs in your browser; your date, time and place are neither sent nor stored. Only your device remembers your last entry, so the next calculator starts filled in, and you can delete it below the form.

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