Western astrology uses a 360-degree wheel to represent the essentials of a horoscope. In my previous posts on aspects and elsewhere, I have used the wheel as a convenient medium to place planets in signs, using the 9 o’clock spot to start the zodiac at 0 degrees of Aries, then sweeping counter-clockwise through the wheel, segmenting it according to the sequence of zodiac signs:
This is the simplest version of the horoscope wheel structure, typically used when the birth time is not known with any reliable accuracy. Planets are then placed in various segments according to their signs, as you have seen previously (the square aspect post, for instance). This rudimentary version of the horoscope can be used in some interpretation, especially for aspects. But many of the details of a full-fledged horoscope are not present in this version.
Drawing a fully accurate working horoscope requires an accurate birth time. Here’s the horoscope wheel for a female–let’s call her Jane Doe–who was born on Jan 1, 2000 in New York, New York, at 2 pm. (If you are not yet comfortable reading the symbols for the planets and signs, please take a look at the Ephemeris post which provides a translation from symbols/glyphs to names.)
(Astrologers will often refer to the wheel as chart, as in “drawing up the natal chart”, meaning construcing the horoscope wheel for the birth. Charts can also be drawn for non-birth milestone events such as marriage, house purchase, relationship compatibility, and various predictions.)
The wheel maps the entire 360 degree sweep of the skies. The horizontal axis that runs through the middle of the wheel is the ascendant-descendant axis. The ascendant is the sign that is rising on the eastern horizon at the time and place of birth – hence the ascendant is also called the rising sign. Here the ascendant has risen through 2 degrees and 54 minutes of Gemini. The opposite end of the axis, the descendant, will be at the same degree position in the sign opposite to that of the ascendant. Here, it is at 2 degrees and 54 minutes of Sagittarius, which is the sign opposite to Gemini. The ascendant is on the eastern horizon at the point where the sign would rise, and the descendant is at the western horizon at the point where the sun would set.
The vertical axis that runs through the middle of the wheel is the MC-IC axis. The traditional or Latin names for these are the Medium Coeli and Imum Coeli, respectively. But astrologers typically refer to them as MC or midheaven, and IC or nadir. The MC is the point that is directly overhead the birth location, and at the time of Jane’s birth, it was on the sign of Aquarius at 9 degrees and 21 minutes. The IC, the bottom of the chart, is the point directly opposite the MC, and is at 9 degrees and 21 minutes of the opposite sign of Leo.
The ascendant, descendant, MC, and IC are called the angles of the chart.
The wheel is sliced into 12 segments, called houses. The houses are numbered starting with the ascendant, going counter-clockwise. Each house represents certain areas of life, and an interpretation of the chart would throw light on how the energies of the planets might impact the significations of the houses.
There are numerous ways in which these slices may be cut, based on the house system that is used. The house system used here is Placidus, which is the default system used by most Western astrologers. In the Placidus system, the houses are not all of equal size. The starting point of each house is called the house cusp, situated at a certain degree position of a sign. Other house systems would in general have different cusps for the houses (different degree positions from Placidus, or a different sign altogether), but no matter which house system is used, the ascendant, descendant, MC, and IC are always the same.
In general, in the Placidus system (and many other house systems), some houses may span more than 30 degrees of arc, others less than 30 degrees. For instance, the 1st house spans the arc from 02 Gemini 54 to 26 Gemini 41, which is a little under 24 degrees. But the 5th house spans the arc from 07 Virgo 34 to 16 Libra 59, which is a little over 39 degrees. The slicing of houses is symmetrical across opposite houses: the arc spans of the 1st and 7th houses are the same, and so are those of the 2nd-8th, 3rd-9th, 4th-10th, 5th-11th, and 6th-12th. This follows from the fact that like the ascendant-descendant which are the cusps of the 1st and 7th houses, and the midheaven-nadir which are the cusps of the 10th and 4th houses, the cusps of all other opposite houses are in the same degree position in opposite signs. However, in other house systems, the ascendant, descendant, MC, and IC may not be the cusps of the 1st, 7th, 10th, and 4th houses, respectively.
In some horoscopes (especially those drawn for births at high latitudes, north or south), the 30-degree span of a sign is entirely contained within a house, with room to spare. This is called sign interception. It happens here, in Jane Doe’s horoscope, in the 6th house, and by symmetry the 12th house. The cusp of the 6th house is in the sign of Libra, and the cusp of the 7th house is in the sign of Sagittarius, and consequently the sign of Scorpio is intercepted in the 6th house. By symmetry, the opposite sign of Taurus (between Aries and Gemini) is intercepted in the 12th house.
Once the angles and the houses are established, the planets are slotted into the various houses according to their sign degree positions. The Lifespan drawing will show retrograde planets with an R next to the position, and the planet itself will be colored red. This is the case of Saturn in Jane Doe’s chart.
There is one additional factor that is typically shown in the horoscope wheel, and that is the north node-south node axis. The nodes are points, not planets, in that there is no active planetary body at those positions. They are the places at which eclipses happen, and like the ascendant-descendant, and MC-IC axes, the north node and south node are at the opposite ends of an axis, so that their positions are at the same degree in opposite signs. Like the sign and planet glyphs, the north node and south node have glyphs as well: the glyph for the north node looks like a pair of headphones, and that for the south node is the same thing, inverted. In Jane Doe’s horoscope, the north node is at 5 degrees and 1 minute of Leo, while at the opposite end is the south node at 3 degrees and 1 minute of Aquarius.
Although the nodes are points, not planets, they are not fixed to a position. Like planets, the nodal axis is in constant motion, with an orbital period of around 17 years. Its actual degree position will vary daily, but because it takes 17 years to do a single go-around of 360 degrees, it only moves about 3 minutes of arc per day. The other interesting thing about the nodes is that they are always in retrograde motion–if someone was born in May 2000, five months after Jane Doe, the north node would have retrograded to the previous sign of Cancer (compared to Jane Doe’s north node in Leo), and the south node would accordingly be in the opposite, and previous, sign of Capricorn.
You’ll notice that not all houses have planets in them, but this does not mean that those houses are irrelevant–they are still tied to planets through their rulerships of the sign that appears on a house cusp. So, for instance, Mercury rules the ascendant (and the 1st house) since the ascendant is in Gemini. The Moon rules the 3rd house since the sign of Cancer is on the cusp of the 3rd house. Astrologers sometimes uses the word ownership or “owns” for rulership, as in the Moon “owns the 3rd house”, or the Jupiter has “ownership of the 8th house”. The concept of house rulerships is a natural extension of the notion of sign rulerships.
Rulerships only apply to cusps–so, although the 3rd house also contains some of Leo, its ruler, the Sun, does not rule the 3rd house. That role is restricted to the Moon. However, there is one exception to the single-rulership rule, and that is when a house intercepts a sign. In which case, it gets two ruling planets: one for the sign on the cusp, and another for the intercepted sign. So the 6th house is ruled by Venus (Libra on the cusp), and Pluto (Scorpio intercepted). Likewise, the 12th house is rules by Mars (Aries on the cusp) and Venus (Taurus intercepted).
In the posts that follow, I will delve into the details of the chart components, starting with the ascendant.