Sunside – Flight Sunlight Visualizer

Sunside helps you decide which side of the plane to sit on by visualizing sunlight along a flight.

https://def324.github.io/sunside/

Demo

Credit / inspiration

Sunside is heavily inspired by sunflight.org. It’s a fantastic tool and deserves the credit for popularizing this “sun side seat” visualization.

As of December 2025, sunflight.org appears to be unavailable. If/when it comes back, it’s worth using. It’s a great reference implementation.

What it does

• Pick departure/arrival airports and local times (per-airport time zones).
• Play or scrub a timeline to see the aircraft move along the great-circle route.
• Visualize the global day/night terminator, a subtle civil twilight band, and the subsolar sun marker.
• See aircraft-local daylight state and relative sun direction (when visible).
• See an aggregate sunlight summary across the whole flight (direction + day/twilight/night breakdown with a compass rose); click it to toggle units (% vs time).
• Share the current flight via a URL (optional autoplay and speed).
• Remembers a few UI preferences in local storage (auto-estimate, distance units, pace, summary units).

On first load, the app defaults to AMS → GRU on today’s date (11:00 departure, 19:00 arrival; local times). Auto-estimate is enabled, but the initial arrival time is a curated example; changing route/departure will apply auto-estimate.

Run locally

Requirements: Node.js 24.x LTS + npm.

npm install
npm run dev

Run the unit tests once:

npm test -- --run

npm test starts Vitest in watch mode (blocks / keeps running).

Full end-to-end rebuild (regenerate data/assets + test + build):

npm run build:all

Documentation

Start here:

• docs/architecture.md
• docs/testing.md
• docs/data-sources.md
• docs/tech-stack.md
• docs/development-notes.md

Notes on accuracy

• Global overlay: day/night (sun altitude > 0) + civil twilight (sun altitude between 0° and -6°) from the subsolar point.
• Sun marker: the subsolar point (sun at zenith).
• Aircraft-local sunlight (day/twilight/night + direction) is computed at the aircraft position using SunCalc.
• Aggregate sunlight summaries are computed by sampling along the flight timeline and rounding to stable integer buckets for display.

AI disclosure

This project is developed using AI models with human oversight. AI assistance is used for things like code generation, refactoring, and debugging; changes are reviewed and validated with tests.