Rising Sign Calculator

Find your rising sign from birth time and place, calculated from local sidereal time rather than guessed.

How this calculator arrives at its answer

The rising sign is the zodiac degree coming over the eastern horizon at the moment of birth. Because the Earth turns a full circle each day, the whole zodiac passes the horizon every twenty-four hours — which is why two people born the same day in different hours have different ascendants.

That also makes it the placement where accuracy matters most. A degree passes every four minutes, so an hour of uncertainty in your birth time can move the ascendant most of the way through a sign.

The default scenario, worked through

The calculator opens with a longitude of -0.13. On those figures the rising sign is ♎ Libra. Underneath, Exact degree comes out at ♎ Libra 11° 05′ and Sun sign at ♊ Gemini 23° 59′. Change any field and every figure updates as you type.

How to fill it in

  1. Enter your birth date and the most exact time you have.
  2. Enter the UTC offset in force at that place and date.
  3. Enter the birth place latitude and longitude.

How the number is calculated

local sidereal time = Greenwich sidereal time + east longitude ascendant = arctan of −cos(LST) over (sin(LST)·cosε + tan(latitude)·sinε)

FAQ

How exact does my birth time need to be?
Within about ten minutes for a reliable degree. Within two hours you may still land in the wrong sign entirely.
Where do I find my birth time?
Usually on a long-form birth certificate or hospital record. Family memory is often out by an hour or more.
Why does latitude matter?
Because the ecliptic meets the horizon at a different angle depending on how far north or south you are, so signs rise faster or slower.