How we compute our horoscopes

By Nadia Reyes

Every reading on this site starts from a computed sky. We calculate where the ten planets actually are for the date, work out what that means for each sign, and write from those facts. The writing is drafted by software against that data, checked by automated validators, and published under a house byline. This page sets out exactly how, including the parts most sites do not discuss.

How are HeyHoroscope horoscopes made?

Four steps, every night, for the following day.

Compute. Ecliptic longitudes for the Sun, the Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto, plus the Moon's phase, any sign changes that day, and every aspect between those bodies.
Describe. The same sky is turned into a per-sign brief: which houses the planets fall in counting from that sign, the condition of the sign's ruler, and which single fact about the day matters most.
Write. The brief goes to writing software, which drafts the four sections in the voice of whichever of our three house writers owns that section.
Check. Automated validators read every draft before it is stored. A draft that fails a hard rule is rewritten once and rejected if it fails again.

Where do the planet positions come from?

From astronomy-engine, an open-source astronomy library. Its planetary positions come from the VSOP87 series, its Moon from E. W. Brown's lunar theory by way of the 1954 Improved Lunar Ephemeris, and Pluto — which VSOP87 does not cover — from a gravitational integration against a precomputed table of states. The library truncates its series deliberately to stay within about one arcminute of error, which is far finer than any astrological reading needs and, being open source, is something anyone can check rather than take our word for.

Positions are geocentric and apparent, referred to the true ecliptic of date. That is the convention Western astrology has used since antiquity, and it is why our figures agree with other astrological software rather than with a star atlas.

We do not compute Chiron, the lunar nodes, asteroids or the four angles. The nodes and the angles are genuinely useful and we would like to add them. We would rather say that than imply a chart we are not casting.

Which zodiac do you use, tropical or sidereal?

Tropical. Zero degrees of Aries is the March equinox, not a fixed star. This is standard in Western astrology and it is the reason your sun sign here may differ from the one a Vedic astrologer gives you — the two zodiacs have drifted roughly twenty-four degrees apart through precession, which is most of a sign.

Neither is a mistake. They are two different reference frames answering two different questions, and the schools that use them have been separate for a very long time.

Which house system do you use?

Whole sign, counted from the sign the reading is written for.

This is worth being precise about, because it is a real limitation. A daily horoscope is written for a sun sign, not for a person, so there is no birth time and no Ascendant to count from. We count the houses from the sign itself: for a Leo reading, Leo is the first house, Virgo the second, and so on. The tradition calls this a solar whole-sign chart. It is what every sun-sign column in the world is doing, whether or not it says so.

What it means in practice: when a reading says a transit falls in your house of money, that is counted from your sun sign. If you know your rising sign, the houses in your own chart will be different, and your own chart is the better guide. Our page on how to read your own birth chart covers that.

How do you decide two planets are in aspect?

By fixed orbs, applied to the five classical aspects.

Aspect	Angle	Orb we use
Conjunction	0°	6°
Sextile	60°	4°
Square	90°	5°
Trine	120°	5°
Opposition	180°	6°

These are tighter than many sites use. A wide orb puts everything in aspect with everything and the reading stops meaning anything, so we would rather report fewer contacts and have them be real.

Two refinements matter. First, where an aspect becomes exact during the day, we find the moment by bisection — narrowing the interval until the angle is as close to exact as the arithmetic allows — so a reading can say when rather than only whether. Second, aspects between two slow outer planets are demoted. Neptune and Pluto can sit in a loose sextile for decades; ranking purely by how close the angle is would promote that over a Moon contact that is actually the news of the day, so our ranking sorts by the speed of the slower body first and tightness second.

What do you do if I don't know my birth time?

Nothing on this site needs one. Every daily reading is computed for a sign, not a birth moment, so no birth data is collected or stored for them.

Our free tools are different — a birth chart needs a date, a time and a place, and the time to the minute, because the Ascendant moves about a degree every four minutes. If you do not know yours, the chart is still worth casting: the planets by sign will be right and only the houses and angles will be uncertain.

Is any of the writing done by a computer?

Yes, and we would rather say so plainly than be found out.

The daily sign readings are drafted by a large language model. It does not invent the astrology: it is given the computed sky and the per-sign brief described above and writes from those facts, in the voice of one of three house writers whose methods and registers are defined in advance. The reference pages in this Learn section, including this one, are drafted the same way and then edited.

What the software does not do is decide what is true about the sky. That comes from the ephemeris. And what it writes is checked before anyone sees it.

Who writes the interpretation, and who checks it?

Our daily readings carry three bylines — Yusuf Karaca, Ines Vasquez and Rhys Calloway — and our articles carry a fourth, Nadia Reyes. These are house voices rather than four separate employees, in the way a magazine keeps a consistent style across many hands. Each has a defined method: Yusuf reads in the classical and medieval tradition, Ines in the modern and evolutionary one, Rhys works with timing and election. Nadia edits. Our About page says the same thing.

We are telling you this because an astrology site that implies four unnamed experts are personally writing your horoscope every morning is doing something we would rather not do.

Checking is automated, and it is worth being precise about what it does and does not catch, because a vague claim here would be worth nothing.

Every draft is validated before it is stored. The validators check that no planet or aspect is named that is not in that day's computed sky; that hedging stays under a set rate; that the reading falls within a length band and that the forty-eight readings of a day vary in length rather than arriving identical; that no reading opens the way more than a set share of the others open; and that a list of machine-sounding vocabulary does not appear. A draft that fails is rewritten once, with the failure quoted back at it.

What happens next is the part most sites would not print. If the rewrite fails too, the reading is kept and flagged rather than thrown away, because the alternative is a missing sign. Those flags are recorded with the day. The only thing that is genuinely never published is a partial day: if the run cannot produce all forty-eight readings, the whole day is withheld and the previous source is used instead.

Two further rules — never predicting an outcome, and never telling a reader what she is like as a statement of fact — are instructions to the writer rather than automated checks. They are the rules we care most about and the hardest to test mechanically, so they are enforced by how the writing is briefed and by editing, not by software. We would rather say that than imply a gate we have not built.

What is computed and what is interpreted?

The honest division, which most sites blur.

Computed, and stated as fact: where each planet is, which sign it is in, its phase if it is the Moon, which aspects are within orb, when an aspect is exact, which planet rules a given sign, and whether a planet is in a sign where the tradition grants it dignity.

Interpreted, and framed as interpretation: what any of that means for a person. Every claim in that second category is the accumulated reading of a tradition, not an observation. We attribute it where we can — to Valens in the second century, to Lilly in 1647, to Rudhyar in the 1930s — so you can see where a reading comes from and how old it is.

We think that distinction is the most useful thing on this page. Astrology's astronomy is checkable and we check it. Its meanings are a body of interpretation built over two thousand years, and whether you find them useful is properly your decision, not ours. Our astrology and science page says where we think the evidence actually stands.