The Mechanics
For a planet to be classified as an out of bounds planet, it must be traveling through our sky at a remarkably high or low angle along the ecliptic--the path created forged by the Sun and Moon, occupied by the zodiacal constellations, that one strip of sky through which the first astrologers noted that stars were moving.
The "bounds" are determined by the Sun's north-and-south range along the east-to-west ecliptic. Go outside for your next visible sunset and mark where the Sun touches the horizon in the west. Some time later (a week, a month, three months), stand in the same place for sunset, and you will notice that the Sun's descension point is either further north or south than when you first saw it. For us living on the northern hemisphere, the Sun is at its northernmost on Summer Solstice, and southernmost on Winter Solstice. The path of the Sun on these polar days creates the "bounds" of the ecliptic, measured at 23.3 degrees north or south (+ or -) in a common declination table.

This is a very surface-level explanation of the mechanics of out of bounds planets. And as much as I enjoy the astronomy realm of astrology, I'm more interested in relaying information about meaning here. So, if you feel the need for a deeper understanding and great visuals, go over to Nick Anthony Fiorenza's The Lunar Planner and learn more.
The Meaning
You or someone you know has an out of bounds planet, but what does that mean?
Meaning! It's what makes astrology astrology.
Really, each out of bounds planet shows its quirky characteristics in specific ways, but there are some thematic commonalities from the Moon on out. For instance, the scofflaw trait.
The Scofflaw Trait
Scofflaw is a term that originated during the American Prohibition era for a person who drinks, shares, or creates alcohol in spite of its illicit status. I like "scofflaw" because it doesn't imply the breaking of a rule out of spite, rebellion, or revolution, but moreso acting outside of a rule because the rule just doesn't make sense. One scoffs at the law, and a "scoff" entails zero explanation.
In this vein, a person with an out of bounds moon simply doesn't heed society's rules when it comes to the realms of home, emotion, caregiving, needs, or instinctual reactions. Apply the same concept to Mercury's realms of communication, magic and information flow, Venus' worlds of taste, creation and relation, and Mars' domains of desire, ambition, will and the assertion/aggression spectrum. A person with one or more of these planets out of bounds isn't resisting society's or your expectations just to prove a point. These expectations simply do not naturally occur to them.
Perhaps directly correlated to the scofflaw trait is the out of bounds planet lifestyle I call living on the fringes.
Living on the Fringes
With my moon out of bounds, I live off the grid in the Appalachian mountains. Some would consider this living far beyond the fringes of society. But, my partner and I are part of a greater community of like-minded folks. We live on the fringes by choosing not to live literally within this community, but rather to come and go as seems fit.
Living on the fringes has many manifestations, though; it isn't always so literal, and just like the scofflaw trait, it is inextricably tied to the domains of the planet who is out of bounds. With the planet Venus out of bounds, a person's romantic relationship(s), or certain components of romance such as affection, may exist in a more private realm. They may prefer art or music that others fail to understand the appeal of, and so typically indulge these tastes in their fringe environment, and around other fringe people with whom they feel comfortable or excited sharing their off-beat tastes. This trait manifests in the astronomy of out of bounds planets, who travel the general path of the ecliptic, but exist in a territory outside city limits. I believe this also lends to another common characteristic: the sight.
The Sight
Think about the planets as living beings in our sky, and the ecliptic bounds set by our Sun as two-way mirrors, such as those seen in interrogation rooms on TV crime dramas. Planets inside the interrogation room (or in bounds) can only see reflections of themselves in these mirrors, but on the other side of the mirror, the out of bounds planet has the sight to observe what goes on within the interrogation room as well as what is happening in their own space.
Furthering this analogy, these mirrors work in such a way because of a trick of lighting. The interrogation room is brightly lit, and the viewing room is dark, only receiving light from the other side of the two-way mirror. If a light is switched on in the viewing room, the transparency of the mirror is lost. And so, it is this existence in darkness, or on society's fringes, that bestows the sight upon the person with an out of bounds planet.
As with any uncommon innate gift, the sight requires development as the person matures into adulthood. A flourishing sense of out of bounds sight allows the person to witness "normal" human behavior and understand conceptually what is going on in the dominant culture, while also maintaining a healthy boundary for them which they can cross back and forth to their liking. However, when an out-of-bounder traverses into the activities of the dominant culture, they do not abandon their sight. They are always witnessing, whether or not they are participating. Of course, there is a lot to witness, and no person can witness it all. The person with an out of bounds planet is by no means omniscient! In fact, they are quite suited to themselves. Each of them notices certain things more than others, and reacts in line with the tendencies shown in their respective natal charts.
Feeling Alien
The sight seems to go hand-in-hand with the out-of-bounds condition of feeling alien. The science fiction/fantasy writer, Taoist and anarchist Ursula K. Le Guin (birth chart) wrote her works of fiction almost exclusively following protagonists who were strangers in a strange land. Her moon is in Gemini, out of bounds, and perhaps not-so-strangely, in exact conjunction with the Gemini moon of science fiction pioneer Robert A. Heinlein (Mars out of bounds) who wrote the 1961 novel Stranger in a Strange Land. Fiction writers are hard-wired to process their own experience of being human in their work. Just know, if you find yourself often questioning--metaphorically--"Am I an alien?" then you may have a planet (or two, or three) out of bounds. And the truth is, you kind of are! Feeling alien can beget feelings of isolation and disconnectedness. In times when I feel this way, I find it beneficial to remember others I know who also fit the description. We are all connected by this little-known (of course!) condition, and each of us carries our own brand of genius.
w/ Love,
Phil
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