What is the colour of the sky?
What colour do you think it is?
I saw some comments from my parents the other day about the colour of the sky here, which they said is always blue and always pretty clear when it’s clear, so I decided to make an app that tracks it and tells me what colour the sky actually is from where we are in the world.
Every day I’m taking one photo of the sky around midday, and then I boil each photo down to a single colour, a kind of average of everything in the frame, which I do again for each week, month and year.
So, why is it blue?
Sunlight looks white, but it’s really every colour mixed together, a bit like a rainbow squashed into one beam, and when that beam runs into the air it bumps into gas molecules that bounce the light off in every direction. Blue light gets bounced around about six times more than red light, so wherever you look in the sky you’re mostly seeing blue that’s been knocked towards your eyes.
You might wonder why it isn’t violet, since violet bounces around even more, but the sun doesn’t give off much of it, and our eyes aren’t great at seeing the little that does make it down, so blue wins. It’s the air doing all the work here, by the way, and not the sea being reflected up into the sky, which is a myth that refuses to die.
Why do I take a photo around midday?
You’ve probably heard that sunsets go red for the same reason, and they do, but sunrise and sunset are a different story that I’m leaving out here, because my photos are taken around midday, when the sun is high and its light has the shortest trip through the air. That keeps the sky close to its bluest, and it means one day is a fair comparison with the next.
What the app will show?
If the sky were simply blue all the time, the colour wouldn’t move much, but I’d bet it does, because cloud drags the average towards grey, and a crisp day after a clearing southerly should come out deeper. So my parents might well be right, but the colours as they build up over time will show how blue it really is here, and how often it isn’t.
Check out the project page or the actual app page.
