What the Rising sign is
The Rising sign, or Ascendant, is the point of the zodiac on the eastern horizon at your birth. Because the Earth turns, a new sign rises roughly every two hours. That makes the Rising sign the most personal of the Big Three: two people born on the same day in the same city can have different Rising signs.
Astrologers read it as your manner: how you start things, how you come across before people know you, and the style you use to meet the world. In whole-sign houses, which this site uses, the Rising sign also sets the first house, so it decides which sign falls in each of your twelve houses.
Why it needs your birth time
The Sun sign barely changes during a day, and the Moon changes at most once. The Rising sign moves through all twelve signs every day. An error of even 15 minutes can change it if you were born near a boundary. That's why this calculator asks for a time and won't guess one. If you mark the time as unknown, it shows your Sun and Moon and leaves the Rising sign open.
If you don't know your time, a birth certificate, hospital record, or baby book is the best source. Some countries record it on the certificate and some don't.
How it's calculated
Your birthplace becomes latitude and longitude, and your local time is converted to universal time using the time-zone rules that applied in that place on that day, including daylight saving time. The Ascendant is then calculated from sidereal time and the obliquity of the ecliptic, the same way any astronomy-based astrology program does it. No paid astrology service is involved, and nothing is generated by AI.
Places very close to the poles are a special case. Some ecliptic degrees never rise there, so the calculator says so instead of giving an unstable answer.