Astrology, done like it matters whether it’s right.

Undersky started from an observation: the web's most-used birth chart sites treat the computation as a commodity and the presentation as an afterthought — mystical wallpaper over decades-old interfaces, noon times silently assumed, precision implied where none exists.

We took the opposite bet. The chart is a computed artifact of the actual sky — the one photographable fact astrology is built on — and it deserves to be computed properly and presented like the beautiful technical document it is.

What that means in practice

Planetary positions on Undersky come from modern astronomical models (the same family used for real ephemerides), computed as apparent geocentric ecliptic longitudes of date, accurate to the arcminute. The engine is tested against events the sky actually staged: equinoxes, solstices, and eclipses. House cusps keep their geometric invariants at every latitude we test — and where a house system genuinely breaks down, near the poles, we say so and fall back honestly.

When you don't know your birth time, we won't invent your Rising sign. You get a solar chart — the strongest chart that's actually knowable — with the Moon shown as its true range for the day. The chart you can trust is worth more than the chart that flatters.

What astrology is, here

We treat astrology as a mirror for self-reflection with twenty-five centuries of accumulated craft — a symbolic language precise enough to be worth computing precisely. We don't treat it as medicine, financial planning, or fate. Nothing on Undersky predicts your future or should stand in for professional advice of any kind.

How this is made

The blog and the words in the interface are written and edited in-house, against a house style guide kept beside the code, and every figure quoted in a post comes from the engine described above. Each celebrity chart page carries a piece about that one chart, committed as fixed text rather than generated while you read it, and checked against the engine by a test that fails our build if the prose and the arithmetic disagree. The Deep Reading is held to the same rule from the other direction: code reads your computed chart and fixes the sections before a word of it exists, and nothing in the finished book can name a placement the chart record doesn't contain.

Articles are published under one byline, Undersky editorial, and show the day they went up, plus the day they were revised once they have been. A piece nobody has touched shows one date. Where an article rests on an outside reference, the reference sits at its foot with a line saying which claim it stands behind.

The instruments

• The calculator — free, complete, computed in your browser.
• The deep reading — a written interpretation of your exact chart.
• The blog — learning the craft, plainly.

Questions, corrections, or a birth-record mystery you're proud of solving: hello@undersky.me

Place names, coordinates, and time zones for the birthplace search come from GeoNames, used under the CC BY 4.0 license. We filter and reformat the GeoNames data for search; any errors introduced by that processing are ours, not GeoNames’.