Which side of the bus is shaded?
Short answer: the side facing away from the sun. The longer answer is that "away from the sun" depends on the time of day, your direction of travel, and what's standing between you and the light.
The simple rule
The sun rises in the east and sets in the west. So:
- Morning — the sun is in the east, so the west-facing side of the bus is shaded.
- Afternoon — the sun is in the west, so the east-facing side is shaded.
- Midday — the sun is high and, in the northern hemisphere, roughly to the south, so north-facing windows stay coolest.
That's the whole idea, and it's enough to make a good guess. The catch is the word "facing": the shaded side isn't fixed to the left or the right of the bus — it depends on which way the bus is pointing.
Why your direction matters
Picture a bus heading east in the morning. The sun is ahead of you in the east, so the windows on the left (north side) are shaded and the right-hand windows catch the light. Now the same bus turns around and heads west in the afternoon: the sun is ahead again, but this time the shaded side is the other one. Same route, opposite answer.
This is why you can't just remember "always sit on the left". You need two things together: the sun's position (azimuth) and the bus's heading. That's exactly the calculation 見光死 Shade Chaser runs for you.
The northern-hemisphere twist
In Hong Kong, Taipei and Tokyo the sun tracks across the southern sky. That means south-facing windows get the most sun through the day, and north-facing windows the least — a handy rule of thumb when the sun is high and you can't tell east from west at a glance.
Buildings, trees and the road itself
Direct sunlight isn't the only factor. A tall building on the sunny side can throw a shadow right across the bus, and tree-lined roads do the same. In Hong Kong the app uses the Lands Department 3D building model to work out where towers actually cast shadow along your route, so it can tell you you'll be shaded even when the raw sun angle says otherwise.
What the app shows
Open a route in the app and it reads the live sun azimuth and altitude for your time and place, matches it to the bus heading, and draws a colour-coded seat diagram — shaded, exposed and neutral zones. As the route progresses it updates, so you can shift seats before the sun finds you.
Ready to go further? Readhow to avoid sunlight on a bus or jump tothe best seat to avoid the sun.
Frequently asked questions
Which side of the bus is shaded in the morning?
In the morning the sun is in the east, so the side facing west is shaded. In the afternoon the sun is in the west, so the east-facing side is shaded.
Is the shaded side always the left or the right?
No. It depends on which way the bus is pointing. The shaded side is simply the side facing away from the sun, so on an outbound trip it might be the left and on the return trip the right.
Why does the shaded side change during the ride?
Because buses turn and the sun moves. A route that loops or doubles back can put the sun on the other side, and over a long ride the sun's angle shifts too.
Do buildings change which side is shaded?
Yes. Tall buildings cast long shadows that can shade a bus even when the sun would otherwise hit it. In Hong Kong the app models this with the Lands Department 3D building data.
