Astronomy & Celestial Mechanics
the sky, computed
How this site is made

The figure library

Every picture here is generated from code at build time. This is the list of generators, grouped by family, with how many essays call each one — which is both the reuse this collection lives on and the blast radius of changing one.

No figure on this site is a drawing that was made once and saved. Each one is a function: it takes parameters and returns SVG, so the same generator produces the orbit at eccentricity 0.6 and the orbit at 0.017 without either being redrawn.

That is the reason the collection can keep growing without the illustrations drifting apart. A generator is written once, checked once, and every essay that calls it inherits the same line weights, the same colour roles, and the same behaviour in dark mode. There are 182 of them, and between them 909 essays call them 1163 times.

The count beside each name is how many essays instantiate it, because that number is the one worth watching. A generator written for a single essay and never called again is a design failure rather than a neutral cost: the whole economy of this collection is that a picture drawn for one argument turns out to be the picture for six. It is also the blast radius — changing a generator changes every figure on its page at once, which is what has to be rebuilt and looked at before the change is believed.

Orbits

Conics, anomalies, elements and transfers — the shape of the answer. — 25 generators.

Gravitation

Fields, barycentres, tides, resonances and the three-body integrator. — 33 generators.

The observed sky

Coordinates, seasons, phases, eclipses and the geometry seen from inside it. — 18 generators.

Starlight

Magnitudes, spectra, blackbodies, parallaxes and the distance ladder. — 20 generators.

Stars

The HR diagram, interiors, lifetimes and the pulsators that measure distance. — 23 generators.

Spaceflight

Burns, budgets, patched conics and the exponential that decides what can be flown. — 16 generators.

Exoplanets

Transits, wobbles, magnifications and the census they add up to. — 14 generators.

Galaxies

Rotation curves, spiral patterns, luminosity functions and the mass that is not light. — 19 generators.

Cosmology

Expansion histories, horizons, acoustic peaks and the abundances left over from three minutes. — 14 generators.

All essays · The fields