The “Big 3” are the 3 major pillars of one’s personality and denote the Sign placements of the Sun, Moon, and Rising/Ascendant, (in that order). For example, if you were born with Libra Sun, Scorpio Moon, and Sagittarius Rising, then your Big 3 would be “Libra, Scorpio, Sagittarius”. 

In the 1900’s, it was common to ask someone for their Sign – “Hey man, what’s your Sign?” 

They were simply asking for the Sign placement or position of one’s Sun.  Knowing someone’s Sun Sign does indeed provide many clues about a person's Ego, lifepath, and the way they shine during this lifetime, but it is only one layer of the Astrological makeup. 

Thanks to software and the Internet, everyone can look up their full natal charts now and have graduated to asking for the “Big 3”.

There are dozens of other things to consider in one’s chart, but the Big 3 provides a quick sense of the Astrological DNA that one has.  (Only 1 in 1728 other people have the same Big 3 as you.)

The Sun represents your fundamental lifeforce, your Ego (identity), your awareness style, and the type of fuel that fuels your creative force (Moon).  It is your core, your structure, and the bones of your soul in this lifetime.

The position of your Sun Sign reflects the primary way in which your lifeforce interacts with the environment.  It represents the personality or traits that you're expected to develop and mature into throughout your life.  Ex: If your Sun is in Virgo, (and you’re 20+ years old), you're undoubtedly more detail-oriented than most other individuals older than you; and this ‘skill’ will become ever more refined as you age.

While your Sun represents the basic shape and structure and willpower of your soul, there are hundreds of other Astrological factors that can color the Astrological calculus of your being.  Ultimately, the Sun is the adult in the room and unless your Moon sign is Water (Cancer, Scorpio, Pisces), it makes the final decisions.

The Moon represents your Id (subconscious), your most primal instincts, and the initial emotional gut-reaction you have to something. 

Your Moon Sign is your style and capacity for emotions and what you feel you need for a sense of security.  It’s your source of hunches, creativity and for things you know without thinking.  Your immediate family and close friends see your Moon side the most because you're less tense around them and don't hide your emotional process.

If your Moon Sign is Fire (Aries, Leo, Sag), then you have “a fire in your belly” (you react passionately when unexpectantly confronted); if your Moon Sign is Air (Gemini, Libra, Aquarius) then you’ll react in a colder and more calculated manner when unexpectantly confronted. 

The Superego is represented by the Ascendant (Asc) Sign also known as the Rising Sign, and is determined from the degree which was exactly on the eastern horizon at the moment and location of one’s birth. 

It represents how we perceive our ideal self to be, as well as how we want to be perceived by others. It is both a mask we wear as well as the lens through which we perceive the world.  Even if you have a poorly aspected, dark and brooding Scorpio Moon, you may still perceive yourself to be an optimist if your Rising Sign is Sagittarius (the eternal optimist).

In Astrology, the planet that rules the Ascendant is the “chart ruler” and the lens through which all other aspects of the chart are focused and considered.   The Rising degree determines the layout of the entire House system in a chart and marks the beginning of the First House, which signifies one’s physical body and style choices - how you present yourself to the world.