The Ascendant is the first sign that appears on the eastern horizon where the Sun rises. Since it is a sign on the rising- the Ascendant is also called the Rising Sign. Of the twelve houses, the Rising sign always takes up the first house (since the signs ascend in succession but houses never move). The first house rules over the head and face. Thus, the rising sign in the first house is connected with the workings of the brain and determines our natural tendencies, self-interest, and worldly outlook.
If the Sun signs reveal outer expression and the moon signs speak of the inner bearings, the Ascendant rules over the way people see you. The first house is the house of self-identity and personality, and thus, the rising sign is associated with your external being. The rising sign gives a quick peek into your personality than the Sun or the Moon sign. The Rising sign and its ruling planet become crucial when it comes down to comprehending your personality. Let's say, for instance, Gemini is the sign in the first house in your astrological chart. Gemini is ruled by Mercury, and Mercury is a planet that has a domain over the nervous system. So, with Gemini in your ascendant, Mercury becomes a crucial planet of influence that will unusually charge up your nervous system. Your brain will be constantly active, and there will be this adrenaline rush that you'll experience all the time! You'll have a quick wit, be charming, and have an exceptional gift for words. You'll have long arms and legs, bright eyes, crave mental stimulation, be restless, dig deep into subjects, and want to know the 'why' of everything.
The Big 3 thus affect the character principally. Usually, the Sun, Moon, and rising signs are different (for any given individual). But, in double placements, the Sun and Moon signs happen to be the same for the given individual. In rare cases, the entire Primal Triad may just take up one sign, constituting the triple placement. For instance, Aries may take up the Sun sign, which happens to be the Moon sign, and might occupy the ascendant or the first house at the same time. If this happens, then it's like a drug effect that has been multiplied three times!
You can determine your Big 3. All you need are the following things:
1) Your time of birth
2) Place of birth
3) As well as your birth date
On your astrological map, locate the signs where the Sun, Moon, and Ascendant lie. You'll thus have three different placements and a corresponding sign for each. Your birth chart has the answers to your questions.
If you locate your Big 3, then your chart will start communicating with you. It will give you insight into your strengths and areas where you need correction, highlight your weaknesses, indicate your strengths, and decode your personality. This aspect of Astrology will not only help you up your game but also enable you to understand the Spirit, your Inner Light, in a rich and joyous way.