NavMuseum · an interactive museum of navigation
The art of knowing where you are
Look north. The point the sky turns around sits exactly as high above your horizon as you are far from the equator. Drag the pin on the globe and watch it climb.
The one idea
Nobody has ever seen their position. They infer it.
There is no instrument that reads out “you are here.” There are only observations, and each one says something narrower: you are somewhere on this circle, along this line, on this curve. Navigation is the craft of collecting such constraints until only one place fits, and of knowing how far to trust it.
This site lets you do that with your own hands, from a star sight to a GPS fix, with the real geometry and the real numbers.
- Pole altitudeA circle of latitude: everywhere the pole stands at that height.
- Star or Sun altitudeA circle of equal altitude, centred under the star, hundreds or thousands of miles across.
- TimeA meridian: the difference between your noon and Greenwich’s noon is your longitude.
- Radio bearingA line of position pointing back to the transmitter.
- RangeA circle around the transmitter (a sphere around a satellite).
- Time differenceA hyperbola between two synchronized stations.
- PhaseA family of hyperbolas, one per cycle: precise, but ambiguous.
- DopplerA cone around a moving satellite’s track.
The story
Chapters§
Each chapter is a short essay built around instruments you can operate. Read them in order, or jump to whatever you’ve always wondered about.
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Chapter 1
Latitude from the sky
The sky turns around one point, and its height above your horizon is your latitude. Read it from the pole star or the noon Sun.
Why does Polaris sit at your latitude? -
Chapter 2
Reading the world
A star rises at the same bearing every night. Navigators in many seas built knowledge on regularities like that, and not all of it is about coordinates.
How did people navigate the open ocean without instruments? -
Chapter 3
Longitude is a clock problem
Longitude is the difference between your local time and Greenwich time. Carry Greenwich in a chronometer, or read it from the Moon.
Why did finding longitude at sea take until the eighteenth century? -
Chapter 4
How a sextant works
Two mirrors bring a star down to the horizon. Learn why the arc reads double, how to read it, and what corrections turn a reading into an altitude.
How does a sextant measure an angle on a moving ship? -
Chapter 5
From a sight to a fix
Every observation is a constraint. A fix is where the constraints agree, and an honest fix says how well they agree.
How does a navigator turn sextant sights into a position on the chart? -
Chapter 6
The invisible lighthouse
Loop antennas, radio beams, LORAN pulses and Decca phase turned invisible signals into lines, circles and hyperbolas on the chart.
How can a radio signal tell you where you are? -
Chapter 7
You have four satellites
Satellites broadcast the time. Your receiver's clock is wrong, so it solves for its own error along with its position, and that takes four satellites.
How does a GPS receiver know where it is, and why does it need four satellites? -
Laboratory
Radio laboratory
A hands-on simulator for bearing, range, LORAN-style time-difference and Decca-style phase fixes, with noise and geometry.
Free play, shareable states -
Reference
Sources and simplifications
Every reference the chapters cite, every simplification the figures make with the real story beside it, and how the numbers are checked.
Plus a glossary of every term
How this is made
Real geometry, labelled simplifications
Every figure runs on a small, open computational core: spherical trigonometry, a solar theory accurate to about a hundredth of a degree, the Yale Bright Star Catalogue, and radio models in physical units. The core is tested against independent calculations, and wherever a figure trades realism for clarity it says so in a Simplification note with the real story beside it.
History gets the same care. Claims are sourced and tagged as documented, reconstructed, contested or illustrative, and navigation is not told as a single march toward GPS. Polynesian wayfinders, Indian Ocean pilots and Norse sailors solved different problems with different knowledge, and they appear here on their own terms.
You will never look at a star, a clock, a radio wave or a GPS fix quite the same way again.