Sunway: Solar Math That Picks the Shady Seat
How we built Sunway, an iOS app that tracks the sun along your route by plane, train, bus, ferry or car, and recommends which side to sit on, with all the solar math running on the device.
5
Transport modes
100%
Solar math on-device
20
Route segments per flight
0
Server calls for sun math
The challenge
"Which side of the plane gets the sun?" is a question travellers search for all the time, and the usual rule of thumb breaks on real trips: routes curve, journeys span hours, and flights follow great-circle paths whose heading changes all the time.
What we built
Sunway answers the question for any trip:
- Five modes of transport: plane, train, bus, ferry and car.
- A clear answer: a left/right split of the sun across the whole journey, such as "72% of the sun on the left", and a seat recommendation.
- A Sun tab: daily sun arcs, golden hour and blue hour, with modes for photography, hiking and mindfulness.
How we engineered it
Our engineers implemented the NOAA solar position formulas directly in Swift, so every calculation runs on the device with no server involved. Car and bus routes come from Apple Maps. Flights follow the great-circle path, split into 20 segments. Each segment is weighted by time spent on it and by sun strength, then compared with the direction of travel.
Results
Sunway shipped to the App Store in 2026. Because the solar math runs on the device, the answer is computed on your phone in moments.