Polar alignment you can do without a steady hand

What evo.polaris is ​

A free, offline, open-source web app that produces the three numbers you dial into a polar-aligned mount: your latitude for the altitude knob, a true compass bearing with magnetic declination already corrected on-device, and Polaris' clock position and radius on the 12-hour iOptron AccuAlign reticle — drawn as well as written.

It is built first for astronomers who cannot crouch behind an eyepiece, hold a phone steady, or hit a small target in the dark. Every app that does this job today costs money and quietly assumes a body that cooperates.

It follows the sign of your latitude into the southern hemisphere, where the answer is not the northern one with a sign flipped: there is no southern Polaris bright enough to use, the reticle circles are a different size, the dial counts the other way, and the chart's handedness flips.

These pages ​

There are three, and they are about the thing rather than a tour of the buttons — the app is designed so that the buttons need no tour.

• Accessibility — the input model, why every button says what pressing it does, why the compass is optional, why night mode is measured rather than styled, and the known gaps.
• Accuracy, and how it is checked — what is validated against what, and the two traps that produce output which still looks correct.
• Deploying — serving it, and the three secure-context APIs that fail silently over plain http://.

Night mode, here too ​

These pages carry the app's night mode: pure red on black, one hue, nothing filled. It is in the navbar beside the light/dark switch.

It is here for the same reason it is in the app. Rods are effectively blind above ~620nm — which is why astronomy has used red light for a century — and dark adaptation takes twenty to thirty minutes to rebuild once it is gone. Reading a dark-grey page with near-white text in a field costs you the same twenty minutes that a white one does. Somebody aligning a mount and then opening these docs on the same phone should not be flashed by the handover.

Running it yourself ​

npm test          # validate the maths against the published sources
npm run serve     # http://localhost:8790

The app is a plain PWA — no build step, no framework, no dependencies — and it works offline once loaded, which is the normal case in a dark field. Bundled data is public domain: the Yale Bright Star Catalog (CDS VizieR V/50, 9,096 stars) and NOAA's World Magnetic Model 2025, valid through 2030. The code is MIT.