Astrologist.com uses a consistent modern Western Tropical astrology framework. This page explains the calculation choices, interpretive approach, and limitations behind the birth chart, compatibility tool, AI astrologer, and educational content.
Astrologist.com practices modern Western astrology using the Tropical zodiac. All planetary signs, the Ascendant and house cusps are calculated in the Tropical zodiac. Sidereal astrology is not used by the standard calculator.
The site focuses primarily on natal astrology: the birth chart and what it can suggest about a person. Our interpretive approach is psychological and evolutionary. We treat astrology as a framework for exploring patterns, tendencies, themes, motivations and potential areas of growth.
A birth chart can describe tendencies, tensions, strengths and recurring themes, but it does not dictate your behaviour, your future or who you are. Interpretations are never presented as deterministic facts.
The standard house system is Placidus.
Placidus houses become unreliable very close to the poles. For birth locations above 66° latitude (north or south), Astrologist.com uses Equal Houses from the Ascendant instead. A latitude of exactly 66° still uses Placidus; the fallback applies only above 66°.
When this fallback is used, the chart tells you so. An Equal House chart is never presented as if it were Placidus. And if a Placidus calculation fails unexpectedly at a location where it should work, the calculator reports a calculation problem rather than silently switching to a different house system.
Signs and houses are separate parts of the chart. Astrologist.com does not teach that Aries literally rules the 1st house, Taurus the 2nd house, Gemini the 3rd house, and so on.
There are historical and thematic parallels between some signs and house topics, and our educational content may discuss them. In modern Western astrology, Aries is often associated thematically with 1st house topics, but signs and houses are separate parts of the chart and the sign does not literally rule that house.
Astrologist.com follows a modern-first rulership system while explicitly retaining the traditional rulers. Three signs have both a modern ruler and a traditional ruler:
| Sign | Modern ruler | Traditional ruler |
|---|---|---|
| Scorpio | Pluto | Mars |
| Aquarius | Uranus | Saturn |
| Pisces | Neptune | Jupiter |
All other signs have a single ruler: Aries (Mars), Taurus (Venus), Gemini (Mercury), Cancer (Moon), Leo (Sun), Virgo (Mercury), Libra (Venus), Sagittarius (Jupiter) and Capricorn (Saturn).
Rulerships are used in interpretation, for example when discussing the chart ruler or the ruler of a house. They describe astrological relationships, not literal physical or psychological causes.
Astrologist.com uses the Mean Lunar Node. The True Node is not used by the standard calculator. Mean Node and True Node are two different calculation conventions; neither is inherently more valid, and we use the Mean Node as our consistent standard.
The North Node and South Node are always exactly opposite each other by definition, so that automatic opposition is not shown or interpreted as a meaningful aspect. The Nodes can still form aspects with other points in the chart.
The Mean Lunar Node normally moves retrograde. Because this is always the case, the normal interface does not show a retrograde symbol (℞) for the Nodes; it is not an unusual condition of your individual chart.
The standard calculator uses the five major aspects, each with a fixed orb (the allowed distance from the exact angle):
| Aspect | Angle | Orb |
|---|---|---|
| Conjunction | 0° | 8° |
| Sextile | 60° | 6° |
| Square | 90° | 8° |
| Trine | 120° | 8° |
| Opposition | 180° | 8° |
These orbs are deliberately flat and fixed. The same orb is used whichever planets or points form the aspect. There is no wider orb for the Sun or Moon and no planet-specific orb expansion. This keeps the chart simple, predictable and consistent.
The standard calculator does not currently distinguish between applying and separating aspects. Minor aspects such as the quincunx, semi-sextile and quintile are not part of the standard calculator.
Chiron is included in charts where reliable Chiron data is available. It forms major aspects using the same orb rules as the planets and Lunar Nodes, with no special wider or narrower orb.
The available Chiron data covers a limited range of dates. If a birth date falls outside that range, Chiron is left out and the chart says so rather than hiding the gap.
Charts with a known birth time and charts without one are treated differently.
If you don't know your birth time, the calculator uses an internal noon reference for the astronomical calculation. Noon is never presented as your actual birth time.
Without a reliable birth time, the Ascendant (Rising sign), Midheaven and house placements are not presented as known.
The Moon gets a special check because it moves fast enough to change signs during a single day. If the Moon could have been in more than one sign on your birth date, the possible Moon signs are shown rather than pretending one is certain.
For simplicity, the standard calculator does not currently apply the same visible day-range uncertainty check to Mercury, Venus, Mars or the other planets. We document this limitation rather than hide it.
The compatibility tool is a sign-level compatibility estimate. It compares the Big Three (Sun, Moon and Rising signs) and the relationships between those signs as a simplified compatibility model.
It is not full synastry. It does not analyse inter-chart aspects, house overlays, Venus/Mars contacts or other full synastry techniques. Known birth times are required for both people, because the Rising sign depends on the birth time.
Astrologist.com is both a calculator and a broad educational resource, so our articles also cover topics the calculator does not compute.
We publish educational content about Lilith, but Lilith is not currently calculated by the Astrologist.com birth chart calculator. No Lilith convention (such as Mean Black Moon Lilith or True/Osculating Lilith) has been selected for calculation. A Lilith placement described in an article has not been calculated for you.
In the same way, articles may discuss minor aspects and other advanced techniques as astrological concepts. That does not mean the standard calculator detects or interprets them.
The AI astrologer works from your actual calculated chart data and follows the same methodology described on this page. It can synthesize a chart and interpret it directly, explaining why an astrologer might reach a particular reading, for example through rulerships, aspects, elements and modalities.
Its wording may vary from one conversation to the next, but your chart facts and the underlying methodology (placements, house system, aspect definitions, uncertainty rules and rulerships) stay the same.
AI readings are interpretive. They are not diagnoses, predictions or certainties. The AI should not claim to know hidden facts about your life that are not supported by your chart or by what you have shared, and it does not treat a placement as proof of how you behave or feel.
We separate two different kinds of information:
Techniques the calculator does not support are never silently presented as calculated. When a limitation applies to your chart, such as an unknown birth time, a high-latitude house fallback or missing Chiron data, we disclose it rather than hide it.
Our methodology changes only through deliberate review, not gradually or by accident. If a core choice such as the house system, Node calculation or aspect orbs ever changes, this page will be updated to reflect it.
For technical information about astronomical data sources and ephemeris attribution, see Astronomy Data Sources.