Understanding how Astrological charts are calculated is essential knowledge for interpreting the information contained in your natal chart, and it's easier to comprehend than you might think!
I recommend you read this blog along with What is True Sidereal Astrology and Understanding Your Sun, Moon, and Ascendant Signs to get the most comprehensive understanding of this cosmic information!
If you’re curious about Astrology then chances are you’ve had your natal chart calculated, whether it be through a free online tool, an app, or by a professional Astrologer, and chances are you were pretty confused at the resulting circular diagram of shapes and symbols—at least at first! Though it seems daunting, understanding how your natal chart is calculated is actually easier than you think.
It is absolutely worth your time to learn how charts are calculated in Astrology if you feel called to explore this modality to any substantial depth. Your natal chart is a map of your energy field, a diagram of the Solar System at the moment of your birth.
It shows the positions of the celestial bodies in relation to each other and their alignment in the sky and constellations when you took your first breath as an individual human being in this physical life, imprinting you with the quantum particles and frequency of that precise moment in spacetime. It’s like your cosmic DNA. I like to call your natal chart your light pattern, as it shows the unique path of photons being reflected from the Sun & Zodiac constellations by all the other celestial bodies in our Solar System. When you understand how the chart is calculated, your ability to interpret the information contained grows exponentially!
There are many free chart calculators online for calculating your natal chart. In fact, if you've used multiple of these online tools, you may notice that some components of your chart change when using different calculators. This happens because there are multiple methods of calculating Astrological charts, including different approaches to the Zodiac and House systems. I discuss this in greater depth throughout this blog. In my professional work with Astrology, I use what is called the True Sidereal Zodiac, and I offer a free chart calculator on my website that uses this approach to the Zodiac. The chart I use as an example here is my personal natal chart calculated using this online tool.
Chart Components & Basic Orientation
Let’s first explore all the pieces to this cosmic puzzle that is the natal chart. We will dissect all of these parts and how they are determined in the chart.
Every natal chart is comprised of several components, including:
The Zodiac system & signs—located on the very outer ring of the chart
The House system of 12 Houses—located on the inner ring of the chart
Planets & Celestial Bodies—seen as various symbols in the chart
Directional axis planes—also seen as various symbols in the chart
Aspect Relationships—the lines in the center of the chart connecting symbols
An important thing to note when looking at your chart is that all components are calculated based on our perspective on Earth. To orient yourself with all the information in the natal chart, the Earth is at the center, even though the Sun is technically the center of our Solar System. We care about where things were in relation to your birth location on this planet. If you're unsure what I mean by this, keep reading, and the following diagrams will help illustrate!
Rotations in our Solar System
What is life but a cycle inside of a cycle inside of a cycle? Another way of describing your natal chart is it is a snapshot of an elaborate, interconnected system of energetic cycles and we are deriving information about you based on the timing and relationship of all of these cycles. We calculate these energetic cycles by analyzing the rotations in our Solar System that structure the very basics of our Earthly life. Two primary rotations in our Solar System are considered when calculating any Astrological chart: the Earth’s annual orbit around the Sun (time of year you were born) and the Earth’s daily rotation around its axis (time of day you were born). These two rotations that we experience are what determine the dynamics of your entire chart, as well as your geographical location on Earth when you were born.
It is worth noting that some branches of Astrology, like True Sidereal, consider a third rotation, a shifting in our Solar System called the precession of the equinoxes created by a wobble in Earth's axis. For this introductory description of how the natal chart is calculated, we will only discuss the two primary rotations taken into account by every branch of Astrology.
The Location of the 1st House, a Constant in all Charts
Now, just about everything can shift when looking at different charts. Some of us have Aries at the top of the chart, some of us have Libra. Some of us have Mercury in our 2nd House, some of us have Mercury in our 11th. Some of us have a lot of lines or aspects in the center of our chart, and some of us only have a few.
There is one constant in every chart that will orient you to the rest of the information presented. No matter what natal chart you look at, the House system always begins with the 1st House (duh) located on the far mid-left side of the chart. This is a significant section of the chart that I will describe more in the following sections.
Even though natal charts vary widely, the 1st House always begins at this mid-left point, and the other houses follow counter-clockwise. Keep this in mind as you continue reading.
Planetary & Other Celestial Body Positions in the Zodiac
So you know how you hear things in Astrology like you have "Jupiter in Cancer" (hypothetically)? What determines whether Jupiter was in Cancer, Virgo, or Scorpio when you were born? If you could look up at the sky and see the planets right now, you would notice they align with certain Zodiac signs/constellations along the ecliptic (shown below). For example, Jupiter is currently in the Aries constellation as I write this blog in April 2024. Anyone born right now would have Jupiter in Aries. About nine months from now, Jupiter will be orbiting in the Taurus constellation, and anyone born at this point in time will have Jupiter in Taurus.
All the planets and celestial bodies orbit around the Sun just as Earth does (minus satellites, like our Moon, which orbits the Earth). The orbital path of all planets roughly travels along a field called the ecliptic plane. The Zodiac signs/constellations, also known as the Zodiacal belt, are located outside the ecliptic plane, like a backdrop of energy interacting with the orbiting bodies in our Solar System. This ecliptic plane is how we can compress a 3D Solar System into a 2D model chart. We are looking specifically at this ecliptic plane of orbiting energy rather than an entire sphere.
The time of year you were born, marking where various celestial bodies were aligned in their orbits along the Zodiacal belt, determines whether Jupiter was aligned with Cancer or Virgo. If you were born a month later, all the planets and other celestial bodies, including Earth, would have moved along their orbital path. The alignment of the planets and other celestial bodies in the Zodiac signs/constellations would change. The degree to which they change depends on the various orbital speeds each of the planets has. For example, Mercury, the closest body to the Sun, orbits the Sun in just 88 days, while Pluto, one of the farthest bodies from the Sun, takes 248 years.
Here's a diagram that looks down on the ecliptic plane, illustrating various planets in orbit and their alignment with the Zodiac on the outside. In this diagram, the Earth is in the middle, even though the Sun is technically the center of the Solar System. This is the same visual point of view we take when looking at the natal chart. The position of all other chart components is taken from our vantage point on Earth and, even more specifically, from the specific geographical location where you were born on Earth.
Your date of birth—day, month, year—determines the Zodiac signs of all the celestial bodies in your natal chart. Are you beginning to see just how many cycles are layered in this chart of yours?
The Orientation of the Zodiac & House System
So, what determines the orientation of the Zodiac signs on the very outside ring? Why is Virgo located at the top left of some charts, by the 10th and 11th House, and the bottom left, by the 2nd and 3rd House, for others? Jupiter could have been aligned with Cancer because of the time of year you were born, but why is Jupiter in Cancer placed in your 6th House and not your 8th House (hypothetically)?
The Zodiac is but another cycle—starting first with Aries, moving to Taurus to Gemini to Cancer to Leo to Virgo to Libra to Scorpio to Ophiuchus to Sagittarius to Capricorn to Aquarius, ending with Pisces. You will always see Taurus after Aries and Capricorn before Aquarius in all charts. Though the Zodiac signs will be listed in the same order on all charts, the orientation of the Zodiac on this outer ring will vary from chart to chart. The orientation of this outer ring of the chart is determined by the time of day you were born. It’s based on the Earth’s daily rotation on its axis, which determines the physical orientation of the sky from your geographical location. Take a look at your chart for a moment. The horizontal line that goes right through the middle of your chart, dividing it into top and bottom halves, was the horizon line of the Earth the moment you were born.
We can only ever see a 180º view of the sky, right? The Earth blocks the other 180º view. We know it’s there; we just can’t see it. So, when looking at your natal chart and the orientation of the Zodiac, any of the signs located on the top half were in the visible sky when you were born, and the signs located on the bottom half were hidden from view by the Earth.
The part of the Zodiac that is in the seen/unseen part of the sky changes as the Earth rotates on its axis every minute. If you were born an hour later, the Earth would have rotated, and the part of the Zodiac that was in the visible sky would have changed, changing the orientation of the Zodiac on your natal chart. The reason you have Aries positioned with your 9th House is because that is where the sign of Aries was located in the section of the sky the moment you were born.
Now, let’s come back to the very significant part of the chart that marks the start of the 1st House, that mid-left point I mentioned earlier. This point marks the Eastern horizon line of the chart, and the opposing right point marks the Western horizon. This horizon line, this boundary that marks the separation of the seen and unseen worlds, is an important threshold of energy in the chart. The Eastern horizon is where the Sun rises, leaving the unseen world of night and entering the seen world of day. The opposite happens at the Western horizon. These two points, the Eastern Horizon and Western Horizon, are one of the significant directional axis planes in the chart, marking what is known in Astrology as the Ascendant (AKA Rising) and Descendant signs.
The Zodiac sign that this Eastern horizon points to is your Ascendant or Rising sign. It’s reflective of how you express yourself. Even if you weren’t born when the Sun was literally rising, the Zodiac sign that this Eastern horizon points to carries that energy of the rising Sun for you. Just as we see the Sun cross from night into day on this Eastern horizon point, the Zodiac sign & energy located here reveals how you take your inner experience of yourself and share it with the external world. How do you filter your self-expression? That’s something your Ascendant sign would tell me.
Likewise, the Zodiac sign on the Western horizon point, your Descendant sign, reveals what you are most receptive and sensitive to regarding information coming into your system, as we see reflected in the Sun leaving the day and entering the night at this point in the chart. Again, even if you weren’t born when the Sun was actually setting, the Zodiac sign on this Western horizon point carries the energy of the setting Sun. Your Descendant sign often correlates with what kind of partnership traits you are naturally sensitive to and harmonize with.
The Eastern horizon point always kicks off the 1st House, which is determined by your time of birth. If you do not know your time of birth, you cannot accurately know your house positions, Ascendant sign, or what part of the Zodiac was in the seen/unseen part of the sky. We are always moving on our axis, so the horizon line shifts slightly from minute to minute. Being even an hour off from your time of birth could produce a significantly different chart orientation.
If you don’t know your time of birth, it’s OK! There is still a lot of information you can derive from your chart. Just get as close as you can. A professional Astrologer can help you narrow in on your time of birth by asking strategic questions. If you desire some help in this department, I welcome you to email me at danielle@sparkyspirit.life
Directional Axis Planes, Continued
We began to explore this component of the chart when I introduced the Eastern and Western points of the horizon line, marking your Ascendant and Descendant signs. Directional axis planes are significant markers of your energy field and what energy is operating where, determined by your time of birth. Directional axis planes do not function in your energy like planets or celestial bodies. These are like paths you traverse, each plane acting like a compass to navigate and channel to express your planetary dynamics. There are two other directional axis planes commonly referenced in Astrology that we will discuss here: the Midheaven (MC) and Imum Coeli (IC), and the Lunar Nodes.
The MC—IC directional plane marks the South and North points of your chart, with the IC marking the Southernmost point in the sky the moment you were born and the MC marking the Northernmost point. If you had looked up the moment you were born, the Zodiac sign of your Midheaven is what you would have seen at the top of the sky, and the Zodiac sign of your IC would have been underneath your feet, due South, unseen beneath the ground. Just like the Ascendant and Descendant signs, your MC and IC signs are determined by your time of birth. What part of the Zodiac was in the visible sky when you were born? It could have changed significantly if you were born an hour later.
The directions of East, North, West, and South are very important when interpreting your natal chart dynamics and are connected to the House positions. The Eastern horizon kicks off the 1st House, the House of Self. The IC kicks off the 4th House, the House of Home. The Western Horizon kicks off the 7th House, the House of Partnership. The MC kicks off the 10th House, the House of Social Contribution.
These North, South, East, and West points tell you where specific energy is operating for you.
Any planet or Zodiac sign near the bottom of your chart, or IC, is inward operating energy and indicates your most innate and natural traits. This energy is correlated with inheritance and roots.
Any planet or Zodiac sign near the top of your chart, or MC, operates externally in your field, outside your physical body, calling you out of yourself and into the material world through this energy to interact. Any planet or Zodiac sign near the threshold of energy marked by the horizon line influences how you process/express information coming and going from your inner and outer experience of self.
A little different than the North, East, South, and West points, the Lunar Nodes are another common directional axis plane in Astrology. They are calculated from the intersection point of two orbital paths: the path of the Moon around the Earth and the path of the Earth around the Sun. There are two points where these orbital paths cross, one marking where the Earth just came (South Node) and one marking where the Earth is going (North Node).
The Lunar Nodes are rooted in Vedic Astrology in the myth of Rahu and Ketu and indicate the longer path of karmic lessons your Soul is harmonizing. The Lunar Nodes are commonly associated with your Soul’s path to evolution and growth, and the position of this directional axis plane is not correlated with any one House position. The North and South Nodes always oppose each other, and they can be located in any House.
The main takeaway from this information about directional axis planes is that these chart components are calculated from your time of birth, determining your physical orientation with the sky at the moment you were born. They operate differently in your energy field than planets and asteroids.
Aspect Relationships Between Chart Components
So, the final piece of the natal chart we haven’t discussed is the aspect relationships between the celestial bodies, which are represented by the lines coloring the center of the chart. Generally, the lines are red, blue, and black. Each of these lines signifies a specific geometric relationship between the two chart components the line connects. For example, you could have two celestial bodies opposing each other in your chart, meaning that the two bodies were located on opposite sides of the Earth in the Solar System when you were born. This opposition is a relationship that creates a certain energy dynamic between the two bodies and influences how each is expressed. Each aspect relationship influences the two celestial bodies involved in different ways.
The four most common aspect relationships in Astrology are:
Conjunctions—when two celestial bodies are aligned in the sky
Oppositions—when two celestial bodies oppose each other in the sky
Squares—when two celestial bodies form a 90º angle in the sky
Trines—when two celestial bodies form a 120ª angle in the sky
Interpreting aspects is an intermediate/advanced practice. To understand how your chart is calculated, all you need to know is that the lines in the center of your chart indicate the aspect or geometric relationships present between the celestial bodies in the sky at the moment you were born, adding to your dynamic and nuanced human expression.
Putting it All Together & Different Approaches to Chart Calculation
OK, so now you hopefully have some idea of how your natal chart is a reflection of the Solar System and how this map of energy is calculated. Let me know how I did by leaving me a comment! Do you have more questions? Ask away.
So you have a Capricorn 6th House Venus? That means you were born during the time of year when Venus was orbiting through the Capricorn Zodiac sign and during the time of day when Venus was located in the part of the chart/sky labeled as the 6th House.
Coming back to a point I made at the beginning of this blog, it is beneficial to know that Astrologers use different approaches to calculating charts, including different Zodiac and House systems. I use what’s called the True Sidereal Zodiac in my chart calculation, while mainstream Astrology uses the Tropical Zodiac. Remember when I mentioned that some branches of Astrology consider three types of rotations when calculating a chart? That applies here regarding the different Zodiacal approaches. If you’re interested in learning more about different approaches to the Zodiac, check out this blog. The three most popular House systems are whole signs, equal signs, and Placidus. Astrologers also consider different celestial bodies for their interpretations. Some Astrologers include asteroids, like Ceres, in their charts, while others don’t. It all depends on the Astrologer.
Don’t worry too much about the different approaches if you are new to Astrology; just know that you may get different charts when using different calculators, and it’s because of everything you just read here :) There isn’t a right or wrong way to calculate charts, just different perspectives for different reasons.
Holistic Interpretation is a Developed Skill
Your natal chart is a complex, layered map of the Solar System at the moment of your birth. Interpreting a single part never does it justice. You can gather specific, deep information about yourself if you know how to interpret all the chart components together holistically. This does require an advanced level of knowledge and that's where I come in! If you seek professional support on your starlit journey to knowing the self, I would be honored to dive into the Stars and Soul with you.
I have two options for diving deeper into this topic with me as your cosmic guide. For $40, I offer 20-minute personal recordings analyzing your chart focusing on a specific topic, like career or love. For a general understanding of the most significant energy in your chart, I recommend a Sun, Moon, and Ascendant sign analysis.
For more profound work and insight, you can book a private 60-minute session with me for $110. I provide you with professional charts in the different systems to keep and use in the future. All sessions include a full transcript, video recording, and resources to apply the information we explore to your life for growth, healing, and Soul alignment.