Where a planet actually is: three frames and one origin

Tell the ecliptic, equatorial and horizon frames apart, and say which astrological claims live in which — including the one your houses are built in.

Lesson 7 of 10 in Astronomy for Astrologers · free to read · no account, no email

Three ways to say the same place

A direction in the sky can be described in more than one way, and astrology quietly uses three of them in different places without usually saying so. Once you can name them, a whole set of techniques stops looking like a grab-bag.

The ecliptic frame measures from the Sun's path: longitude round it, latitude off it. This is the chart's frame. Everything in the wheel — every sign, every degree, every aspect — is an ecliptic longitude.

The equatorial frame measures from the Earth's equator projected outward: right ascension round it, declination north or south of it. This is the frame telescopes and star catalogues use, and it is where out-of-bounds planets, parallels and contraparallels, and the fixed stars actually live.

The horizon frame measures from where you were standing: azimuth round the horizon, altitude above or below it. This is the frame of what you could have seen, and — this is the sentence to keep — it is the frame your houses are built in.

Behind all three sits a choice that is not a frame at all: the origin. Astrology is geocentric because it is describing the sky from where somebody stood. The engine computes heliocentric positions first, because that is where the physics is simplest, then translates them to the Earth. Both are true; they answer different questions, and a heliocentric chart is a different technique rather than a correction.

Declination: the number the chart does not print

Your chart gives you longitude. It does not, usually, give you declination, and a surprising amount of technique is hiding in the gap.

For a body sitting exactly on the ecliptic the two are locked together: 0° Cancer is always +23°26′ of declination, 0° Capricorn always −23°26′, both equinox points always 0°. That is why the Sun's declination is completely determined by its longitude, and why the seasons and the zodiac are the same story told twice.

For everything else the link is loose, because the body is a few degrees off the line. Which means two planets can share a longitude — a conjunction — while sitting several degrees apart in declination, or share a declination while being nowhere near each other in the zodiac. The second case has a name: a parallel, treated by many astrologers as conjunction-like, and it is invisible in a normal wheel. Contraparallel is the same thing with opposite signs of declination.

And out of bounds, from the tilt lesson, is a pure declination claim: a planet whose declination exceeds 23°26′. You cannot see it in the zodiac at all. It is a fact from another frame, which is exactly why it feels like it comes from nowhere when an app badges it.

Altitude, and why houses need your place

Here is the sentence that makes the next module inevitable. Signs live in the ecliptic frame; houses live in the horizon frame.

The Ascendant and Descendant are where the ecliptic crosses your horizon — the two points at altitude zero. The Midheaven and IC are where it crosses your meridian, the north–south line through the point overhead. Those four points are the joints where one frame is bolted to another, and it is why the signs need only a date while the houses need a time and a place. The zodiac is the same for everybody alive at a given moment. The horizon is yours alone.

It also tells you, straight off the wheel, something you could have seen with your eyes. The half of the chart from the Ascendant up over the Midheaven to the Descendant — houses seven to twelve — was above the horizon at your birth. Houses one to six were below it, under your feet, on the other side of the Earth. So a chart is not only symbolic geometry; it is also a record of what was up and what was down, and you can read that in one glance.

Which is the hinge into the traditional material later in this course. Combust, under the beams, heliacal rising — a planet lost in the Sun's glare, or first visible again before dawn — are all claims about visibility, and visibility is an altitude-frame idea. They look arbitrary in a longitude-only world and completely sensible once you know somebody was standing outside, looking.

What that looks like

One planet, three true statements. Mars at 25° Gemini: that is ecliptic longitude 85°. Its declination that day is about +24°, which is past the Sun's limit — so it is out of bounds, a fact you cannot see in the sign or degree. And at the moment of the birth in question it was 18° below the horizon, in the fourth house, invisible. Nothing contradicts anything. Three frames, three answers, three different bits of astrology.

What to take away

• Three frames: ecliptic (longitude and latitude), equatorial (right ascension and declination), horizon (azimuth and altitude). A chart's wheel is entirely the first one.
• Declination is a separate number the wheel does not print, and out-of-bounds planets, parallels and contraparallels all live there.
• Houses are built in the horizon frame, which is exactly why they need your time and place while the signs do not.
• Houses seven to twelve were above the horizon at your birth and one to six below it — a visibility fact readable straight off the wheel.

The common mistake

Mixing frames without noticing: reading a declination as though it were a zodiac position, or expecting a conjunction in longitude to mean two planets looked close together. Each frame answers its own question correctly and none of them can be substituted for another.

Try it on your own chart

Look at your own wheel and mark which planets sit in houses seven to twelve. Those were above the horizon when you were born: they were, in principle, in the sky. The rest were beneath your feet. Then find your Sun. Whether it was up or down is the single question the whole of Sect turns on later in this course, and you have just answered it by reading a frame.

Check yourself

The same questions the lesson asks in the app. Open one to see the answer.

Keep going

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