Helios is a web application that tells you which side of a vehicle to sit on during a trip — left or right — based on where the sun will be throughout your journey. Whether you want full sun or complete shade, Helios works out the answer for you by combining solar-position calculations, great-circle routing, and your trip’s departure time and direction. This matters more than it might seem: photosensitive skin conditions, circadian disruption from blue-light exposure, solar charging for devices, or simply comfort on a long train or bus ride are all real reasons to care which side of the vehicle faces the sun.Documentation Index
Fetch the complete documentation index at: https://mintlify.com/V3RNE42/helios/llms.txt
Use this file to discover all available pages before exploring further.
What Helios does
Helios guides you through a three-step wizard before calculating a result:- Preferences — Choose whether you want sun or shade, whether you can change seats mid-journey, and whether you want results expressed in local time (adjusted for time-zone crossings).
- Origin — Enter your departure city and country, along with the date and time you leave.
- Destination — Enter your arrival city and country, along with the expected date and time of arrival.
| Left | Right | Condition | Direction |
|---|---|---|---|
| ☀️ Sun | 🌑 Shade | Before solar noon | North → South |
| 🌑 Shade | ☀️ Sun | Before solar noon | South → North |
| 🌑 Shade | ☀️ Sun | After solar noon | North → South |
| ☀️ Sun | 🌑 Shade | After solar noon | South → North |
Assumptions
Helios produces accurate, useful results within a defined set of modelling assumptions. Understanding them helps you interpret the output correctly.- Straight-line route. The trip is modelled as a great-circle path between origin and destination coordinates. Curves, detours, and waypoints are not taken into account.
- Constant speed. Acceleration, deceleration, and stops (e.g. at stations or traffic lights) are not modelled. The vehicle is treated as moving at a constant speed from departure to arrival.
- No terrain, weather, or atmospheric events. Changes in altitude, tunnels, cloud cover, shade cast by buildings or terrain features, and eclipses are all outside the scope of the model.
- Departure-point time zone as reference. All times are initially expressed in the UTC offset of the origin. If you opt in to local-time adjustment, Helios will shift event times to the UTC offset at each point along the route — but only if origin and destination differ in UTC offset.
Because Helios assumes a straight-line route, results are most accurate for
relatively direct journeys such as long-distance trains, intercity buses, or
flights. For routes with significant curves or many stops, treat the output as
a useful approximation rather than a precise minute-by-minute schedule.
When Helios is useful
Helios was built for any traveller who has a reason to care about the sun’s position during a trip:- Photosensitive skin conditions — conditions such as lupus, rosacea, or xeroderma pigmentosum make even incidental sun exposure through a window medically significant. Helios lets you plan your seat choice before you board.
- Solar charging — if you carry a solar battery pack or simply want to use a window seat to top up a device, Helios tells you exactly which side will receive direct sunlight and for how long.
- Circadian rhythm and blue-light management — afternoon sunlight exposure through a west-facing window during an eastbound journey can disrupt sleep schedules. Knowing which side to avoid helps travellers manage light exposure intentionally.
- General comfort — no special medical reason needed. Long journeys in direct sun are simply uncomfortable, and Helios makes it easy to pick the cooler, shadier seat.
Get started
Install dependencies, configure your API keys, and run Helios locally with
vercel dev in under five minutes.Core algorithm
Dive into the solar-position logic, great-circle interpolation, and the
computeRouteSections function that powers every result.