About NavMuseum

This site exists because of one question that turns out to be bottomless: where am I, and how could I possibly know? Every answer people have found, from a star’s height to a satellite’s timing signal, converts something you can observe into a constraint on where you can be. The aim here is to let you see and operate those conversions yourself, with real geometry and real numbers, and to tell their history carefully.

What it is§

An interactive museum in chapters. Each chapter is a short essay built around figures you can drag, play and break: a sky that turns over your head, a sextant whose mirrors pivot, a chronometer you can let drift, radio pulses spreading from transmitters, four satellites and a receiver clock that won’t agree with them. A separate laboratory lets you play freely with radio position fixing. Every figure has a Share button that copies a link to its exact state, so you can send someone the precise thing you’re looking at.

It is free, has no ads, needs no account and sets no cookies of its own. It is written for curious adults: engineers, sailors and pilots, amateur astronomers, radio people, teachers and anyone who prefers to understand a mechanism rather than memorize a fact.

How the figures are computed§

All figures run on a small open computational core in plain JavaScript, separate from the drawing code, so the same function that draws a circle of position is the one that is tested. The core includes spherical trigonometry for the navigational triangle; a solar theory after Jean Meeus’s Astronomical Algorithms, accurate to about 0.01° for the Sun and a few seconds for the equation of time; precession of the equinoxes; star positions and brightnesses from the Yale Bright Star Catalogue; coastlines from Natural Earth; and radio and satellite models in SI units.

The core is checked two ways. Its own tests cover invariants and worked examples. Separately, an independent test suite, written without reading the core’s source code, recomputes results from the published formulas and reference values (almanac-style solar positions, the double-reflection law of the sextant, hyperbolic time differences, satellite pseudorange solutions) and fails if the two disagree beyond stated tolerances.

Wherever a figure trades realism for clarity, a Simplification note says what was simplified and what the real story is. These are collected on the sources page. Nothing here is fit for real navigation: carry proper charts, an almanac and working instruments.

How history is handled§

Navigation is often told as a single march from “primitive” methods to European instruments to GPS. That story is wrong in its shape. Polynesian and Micronesian navigators, Indian Ocean pilots, Chinese compass users, Norse sailors and many others solved different problems with different knowledge, often superbly. Here, traditions are described on their own terms, historical claims are cited, and each is tagged by the strength of its evidence: documented reconstructed contested illustrative. Teaching models are labelled as teaching models, not reconstructions.

The chapters on living traditions have not yet been reviewed by practitioners of those traditions. That review is sought, and corrections are welcome.

The name§

NavMuseum is a museum in the sense that matters: a place to stand in front of real instruments and real problems, except that here you can pick the instruments up. Its galleries are the chapters, its exhibits are the figures, and every one of them works.

The motto, “the art of knowing where you are”, is a fair description of what navigators actually do, which is less like reading a gauge and more like reasoning under uncertainty: gathering partial evidence, weighing it, and committing to an estimate you know is imperfect. E. G. R. Taylor’s classic history of navigation called it “the haven-finding art”; the motto is a nod to that tradition of naming the craft for what it does.

Credits and licences§

• Text and figures: CC BY 4.0. Code: MIT, at github.com/bberg/celestial-navigation.
• Star data: Yale Bright Star Catalogue, 5th revised edition (Hoffleit and Warren, 1991), via a public JSON conversion.
• Coastlines: Natural Earth 1:110m (public domain), packaged by the world-atlas project (ISC).
• Map projections: d3-geo and topojson-client (ISC licence).
• Type: Instrument Serif, IBM Plex Sans and IBM Plex Mono, all under the SIL Open Font License.

Some excellent work this site builds on and links to: Bartosz Ciechanowski’s interactive GPS essay, the Smithsonian’s Time and Navigation, Jerry Proc’s hyperbolic radionavigation archive, and Bowditch’s American Practical Navigator.

Contact§

Corrections, suggestions and practitioner perspectives are very welcome: [email protected]. See also the contact page.