How to find your rising sign: what data you need and why it changes every two hours

Your rising sign, or ascendant, is the zodiac sign that was coming up over the eastern horizon at the moment and in the place where you were born. It is the point of the birth chart from which the houses are built, and that is why it is one of the three things people name most when they describe someone: "Sun in this sign, Moon in that one, rising in the other."

It can't be worked out from your Sun sign, and it can't be guessed "more or less". It is calculated, and for that you need three pieces of data.

What you need

• Your date of birth. It sets where the Sun was and which part of the year the rotation falls in.
• Your time of birth, as exact as possible. It's the piece of data that weighs the most, as you'll see below.
• Your place of birth. The city, because the horizon depends on latitude and longitude. Two people born at the same instant in different cities can have different rising signs.

With those three, the local time is converted to universal time (using the time zone and the daylight saving time in force that day in that place) and the engine works out which degree of the ecliptic was crossing the eastern horizon. That degree is your rising sign.

Why it changes about every two hours

The Earth turns once on its axis in a day, so over 24 hours all twelve signs rise over the eastern horizon, one after another. That gives the best-known rule of thumb: on average, one sign every two hours.

In practice it isn't even. For a single day in New York, March 15, 2024, the engine gives:

• 5:00 a.m. → Aquarius, 4°49′
• 8:00 a.m. → Aries, 16°29′
• 10:00 a.m. → Gemini, 0°18′
• 1:00 p.m. → Cancer, 14°34′
• 5:00 p.m. → Virgo, 2°17′
• 9:00 p.m. → Libra, 19°53′

That day Pisces and Aries each stayed on the horizon a little over an hour, while Leo, Virgo and Libra stayed about two and a half hours. How long each sign lasts depends on the time of year and on latitude: at higher latitudes the difference between them is even bigger.

The same moment, a different place

That same March 15, at 8:00 a.m. in New York, the rising sign is:

• in New York: Aries, 16°29′;
• in London: Cancer, 21°43′;
• in Sydney: Sagittarius, 12°13′.

It is the same instant and the same sky, but three different horizons. That is why a calculator that only asks for date and time can't give you your rising sign.

How much error your time can take

The rising sign moves roughly one degree every two to five minutes, depending on the sign and the latitude. With that pace, an approximate time is enough to know the sign in most cases, but not the degree or the house each planet falls in.

For the same New York example, from 8:00 a.m.:

• 8:15 → Aries, 22°44′
• 8:30 → Aries, 28°48′
• 9:00 → Taurus, 10°16′
• 10:00 → Gemini, 0°18′

If you were born close to the change from one sign to the next, half an hour of difference in your time can change your rising sign: in this example, between 8:30 and 9:00 it goes from Aries to Taurus. If you're in the middle of a sign, it doesn't move at all. The best thing is to have the time that appears on your birth certificate. If you don’t have it, we explain what you can still read without it.

If you don't have your time

Without the time there is no rising sign. What you can still calculate is the rest of the chart: the position of the planets in the signs and the aspects between them. The Moon changes sign about every two and a half days, so you can almost always tell which sign it was in too. What you lose are the houses and the rising sign.

Calculate it with your data

In the ASTRA calculator you enter date, time and city, and in seconds it shows your chart with the rising sign and the twelve houses. It is the same calculation we used for the examples above.