The Rising

How We Calculate Rising Signs

A rising sign — also called the ascendant — is the zodiac sign on the eastern horizon at the exact moment and place of your birth. Here is exactly what we need and how the calculation works.

Step 1: Birth date

The full date of birth — day, month, and year. This is used to calculate the positions of the sun, moon, and planets, and to determine the Julian Day Number for sidereal time calculation.

Step 2: Birth time (exact, to the minute)

This is the most critical input. The ascendant moves approximately one degree every four minutes and changes sign roughly every two hours. An error of even 30 minutes can mean a completely different rising sign.

Where to find your birth time: birth certificate, hospital records, or family records. If your birth time is listed as "AM" or "PM" without a specific time, or if you simply do not know it, an accurate rising sign cannot be calculated.

Step 3: Birth place

The city or town where you were born. This is used to determine two things:

  • Geographic coordinates — latitude and longitude of the birth location
  • Time zone — to correctly convert local birth time to Universal Time (UTC)

Two people born at exactly the same moment but in different locations will have different rising signs because the ascendant is calculated relative to the local horizon.

The calculation

  1. Convert local birth time to UTC using time zone + historical daylight saving data
  2. Calculate the Julian Date for the birth moment
  3. Compute Greenwich Sidereal Time (GST) from the Julian Date
  4. Convert GST to Local Sidereal Time (LST) using birth longitude
  5. Use LST and birth latitude to find the ecliptic degree on the eastern horizon (the ascendant)
  6. Map that ecliptic degree to a zodiac sign (0–29° per sign)

Why we need all three inputs

Without birth date: no planetary positions, no sidereal time baseline. Without birth time: the ascendant is undefined — it could be any of the 12 signs. Without birth place: no local horizon, no accurate time zone conversion.

This is why The Rising does not offer "sun sign rising" approximations or birth-time-optional calculations. We show only what can be accurately computed.