# FlightSide is live

[Alex](https://alexcloz.com) here.

This is the first post on the FlightSide journal. I'll use it to share updates, experiments, and small aviation things I notice while building the project.

The first version of FlightSide is now live.

FlightSide answers a simple question I kept running into when booking flights: which side of the plane gets the sunlight? If you like window views this can matter quite a bit. Sometimes you want the light for photos or scenery. Sometimes you prefer shade, like I do.

There used to be a small tool that showed the sun along a flight route and helped you figure this out. It was simple and surprisingly useful. Over time it stopped being maintained and eventually stopped working. I kept thinking someone would rebuild it. Eventually I realized nobody had, so I started building my own version.

## What FlightSide does

You pick two airports, set a departure date and time, and enter the approximate flight duration. FlightSide then shows your route on a map together with the sun's position, the moving day/night line, and a recommendation for which side of the plane is more likely to get sunlight.

![FlightSide full page: LAX → JFK route, sun and day/night line, seat recommendation](/images/journal/001-its-alive/full-screenshot.jpg)

## Follow the flight

One thing I wanted was the ability to see how the light changes during the flight. There's a time slider that lets you move through the trip from takeoff to landing. As you drag it, the aircraft position moves along the route and the sun and day/night line shift across the map.

![Time slider: aircraft marker along the route, sun and day/night line](/images/journal/001-its-alive/flightmap.jpg)

Times are shown in each airport's local timezone so they match what you actually see on your ticket.

## A simple example

Imagine a late morning flight from Seattle to San Diego (for example, [an 11am departure](/SEA_SAN_20260715_1100)). You might take off with the sun on one side of the aircraft. As the flight continues south the angle of the sun shifts, and depending on the season the day and night boundary can approach the route as well.

By the time you are nearing San Diego, the light can be coming from a very different direction than it was at departure. FlightSide lets you see that progression before the flight even happens.

## A couple quick notes

**Overnight flights**  
Yes, it works the same way. You can see when the route passes through darkness and when dawn or dusk crosses the flight path.

**Clouds**  
FlightSide shows where the sun is relative to the aircraft. During daylight, the side facing the sun is usually the brighter side of the cabin, though clouds can soften the light.

One small aviation detail I've always liked: on westbound evening flights you can sometimes watch the sunset for a surprisingly long time because the plane is flying with the moving day and night boundary. It can feel like the sun just hangs outside the window.

## Why the sunny side matters

The sunny side of a flight is not always the better side. Bright light can make photos and views better, especially around sunrise or sunset. It can also mean glare on a screen, a warmer window, or a shade that stays closed for most of the trip.

The shaded side is usually better for sleeping or working. On some flights the difference is obvious. On others, especially around midday, neither side gets much direct light.

## Time of day changes the answer

The same route can feel different in the morning, afternoon, and evening. A sunrise flight can put the light low and forward. A midday flight may put the sun high overhead. An evening flight can stretch sunset across a long westbound route.

That is why seat-side advice is hard to guess from the route alone. Direction matters, but timing matters just as much.

## Flight paths are not flat-map lines

Long flights rarely follow the straight line you would draw on a flat map. They follow great-circle routes, which can arc north or south before reaching the destination. That curve changes which side of the aircraft faces the sun during the flight.

This is most noticeable on ocean crossings and high-latitude routes, where the path can look surprising if you are used to road-map geometry.

That's the first version of FlightSide. Try a route you have taken before and see whether the side you picked matches where the sun actually was.

More updates soon.