How the charts are calculated.

This page states how the numbers on Cosmic Meridian are made. The table at the end lists the claims that have a receipt: the file that backs each one and the date it was last checked.

The ephemeris

Every position comes from the bundled library astronomy-engine 2.1.19, running in your browser. Nothing is fetched from an ephemeris service when you calculate a chart.

The same library, run offline, produces the almanac behind the daily, retrograde and void-of-course pages.

Zodiac and coordinates

Positions are tropical, so each sign is an arc of thirty degrees counted from the March equinox point, not from a fixed star.

Coordinates are geocentric apparent ecliptic of date. That means the planet as seen from the centre of the Earth, corrected for aberration, measured along the ecliptic of the date.

The lunar nodes are the mean nodes, not the true nodes.

House systems

The chart offers these house systems: Placidus, whole sign and equal. Placidus is the default when a birth place and a verified birth time are given.

Placidus cannot be solved near the poles. From 66° of latitude the chart falls back to whole sign, offers whole sign and equal houses, and says so beside the wheel.

Daily texts for your sign use whole-sign houses, counted from your Sun sign as the first house. The Ascendant and Midheaven use the true obliquity of the date.

Without a verified birth time the chart draws no houses and no rising sign.

Aspects and orbs

An aspect is counted when two of the 10 bodies lie within the orb of its exact angle. The orbs are fixed and are the same for every body.

In a chart, a pair is called applying when the gap is narrowing one hour later, judged from each body's own speed.

Time zones and places

City search runs on a gazetteer bundled with the site, so the place you type is not sent anywhere.

A birth time is read as wall-clock time in the place's IANA time zone. It is converted to UTC with that zone's historical rules, including past changes of offset and daylight saving.

For 15 zones, before 1970, the conversion uses a bundled copy of the IANA backzone data. A standard time-zone build merges those zones into a neighbour's history.

If a clock change makes a birth time happen twice, the form asks which occurrence applies. If a clock change skipped that time, the form asks you to confirm the corrected time.

If you do not know the birth time, the chart shows the possible positions across that local day instead of a single point.

Precision and checks

Positions are shown to the arcminute. A sign boundary is decided on the rounded value, so a sign and its degree never disagree.

Tests compare the engine with published tables instead of with itself. Mercury stations for 2026 and 2027 agree to within 6 hours. Lunations from September 2026 to December 2027, and the equinoxes and solstices of 2026 to 2028, agree to within 10 minutes.

Void-of-course windows for September and early November 2026 agree to within 5 minutes. Every eclipse from 2026 to 2028 falls on the published day with the published type. The tables come from Fred Espenak's phase catalogue, NASA's eclipse tables, public Mercury retrograde calendars and the Cafe Astrology void-of-course tables.

How the texts are written

The daily horoscope texts, the event pages and the chart readings are drafted with the help of AI.

The daily horoscope texts are written from the engine's computed facts, and an automated check compares each date, sign, aspect and phase in them with the engine. The event pages are written from the engine's computed facts and checked against it by a script of their own.

The chart readings are fixed texts, written once and tested for banned phrases and repetition. They are chosen by your calculated placements.

On the sky pages, dates, degrees and signs are inserted from computed facts and are never typed by the writer. Your birth details are never sent to an AI service.

Corrections

If a figure here or on another page looks wrong, write through the contact page and name the page and the figure. Please send no birth details.

Cosmic Meridian checks the claim against the engine, corrects the page and records the date of the check. The table below lists each claim on this page, the file that backs it and the date the claim was last checked against that file.