Full credit for the following goes to Jungian author, Karen Hamaker-Zondag in her book "Foundations of Astrology." The concept, itself, is actually very ancient - but I'd never made the necessary cognitive leap to connect it with the astrological birth chart. And possibly, much to her sense of trepidation and dismay, I have - in customary Dr Z fashion - expanded freely on her idea at some length.
Imagine
Imagine in your mind's eye that you're now living in a far off, distant kingdom during medieval times. It's a remarkable, wondrous, and magical land of kings, queens, knights, nobles, jesters, dragons, castles, and such. You're on a long journey across the land... and coming to the top of hill - in the far off distance - you can just make out a magnificent castle.Straining to see - you can see a large tower with its "standard" (flag) flying in the breeze. The "standard" is an emblem that reveals the "community standings" and "identity" of the castle owner to all those that are approaching from a great distance. The standard tells you in broad, general terms whether the owner of the castle is "friend or foe"....
The Standard
The "standard" of this castle is similar to a point in a birth chart called the Midheaven. If you're unfamiliar with astrology - then you've probably never even heard of the Midheaven. Generally, the Midheaven is a point on your birth chart that reflects your public "reputation" and/or how you'd like to be known or seen by others.

The Midheaven is the flag you proudly wave from the highest tower of your castle that tells other folks something about who you are while they're still approaching from a great distance. Very often it reflects your chosen career or perhaps, some other avocation or interest to which you ascribe import.

The Midheaven closely resembles the Jungian term, "the persona." The persona is the outer, external mask that we each construct to protect the true "inner core" of our psyche from the everyday, bumps and bruises of the external world. The "danger" (in Jungian thought) of the persona is when we sometimes end up "identifying" with the mask that we've constructed for society's sake. We start believing the protective mask we've constructed is the "real us." We, then, ignore/repress many of our true needs, desires and wants. This refusal to give "life" (or expression) to our basic needs and desires - then results in a whole host of problems.

But let's continue on to meet another facet of the "persona" called the Ascendant or Rising Sign....
Imagine again...
You decide to continue on the journey, with the intent of meeting and visiting with the landlord of the castle.... After making your way down the hill, you reach your destination. Now, the stately castle stands before you.

Since you're a lot closer, now - you can check out the castle in greater detail: how large is the castle, what's it made of, how's the upkeep of the grounds (have they mowed the lawn, lately)?But before you can go in the castle - you still have to pass over the drawbridge and the portal.

So, all this checking out of the exterior of the castle, the grounds and the drawbridge gives you your first impression of the castle. Long before you ever knock on the door - you've already formed a mental picture regarding whether the castle is inviting, forbidding, well kept, or whatever....

Short excerpt from Foundations of Personality - Karen Hamaker-Zondag

"The exterior of the castle, the drawbridge, the portal, etc. are analogous to the Ascendant of the birth chart. Like the drawbridge, the Ascendant is that part of us that people first see when they're getting to know us. The Ascendant reflects a person's natural way of acting, his/her habitual external behavior, and his/her way of responding to new impulses and impressions.

The Ascendant plays a very unique role within the horoscope. It reflects the psychic content that determines how we manifest ourselves externally. It is an important part of our character, sometimes so natural that when people call attention to our traits, we often have difficulty in recognizing these traits as being a part of us or being 'like us.' Only when we have carefully observed ourselves over a period of time, will the Ascendant characteristics become clear to us."

Step Further....
As mentioned earlier, many astrologers generally agree with the possible harmful effect of individuals who end up one-sidedly identifying with the energies of the Ascendant and/or the Midheaven. It results in the individual not allowing the expression and formation of the energies related to the Sun's placement. You don't let the true you shine out!

However, having said that.... It shouldn't be a case of choosing one or the other (i.e. the Sun or the Ascendant).... It's important to give "voice" and expression to all the many differing (possibly conflicting) characters contained within the Castle of the Psyche. Each part of the horoscope plays its own vital role....
Outside vs Inside


The image you had prior to entering the castle may, in fact, be very different than what's inside. From the outside, the "persona" of the Castle may have looked quite dark and ominous. But upon entering, you might discover it to be quite the opposite.

From the outside, the Castle might look quite well kept and orderly - the inside might be quite another matter altogether.
Inside the Castle
(or don't hate me, Karen H-Z)
Once inside the Castle... we meet the King, the Queen, the King's Magician advisor, and the Court Jester. We also meet the King's beautiful young daughter and a spirited, brave knight. Depending upon the particular kingdom in question, the King may (or may not) be asserting his true, royal right of being in charge of the castle. The inhabitants of the castle may be living in relative peace and harmony - or there may be chaos and unrest - or as with most castles, it's a little both....

In the birth chart
the king is reflected
by the Sun

the queen is reflected
by the Moon

the magician and the jester is reflected by Mercury

the king's daughter is reflected
by Venus

the king's knight is reflected
by Mars.
At this point, I'm going to resist the (royal) temptation of explaining the roles of the different characters that reside within the castle. I think the characters of this grand story speak well enough for themselves. And any attempt on my part to elucidate on the meanings of the characters (especially in this short space) would serve only to severely limit their true natures and potentials within the Castle of the Psyche called the horoscope....