Why a single light pole isn’t visible from space but a city full of individual ones is?


I can’t wrap my head around this. The light poles are still emiting light individually, so how do they get merged into one single source of light when viewed from space and become visible? It feels logical to me that one light pole should look the same as a hundred thousand since they’re just a repetition of one light pole with each one acting separately.

In: 10

i would assume its the same concept as you looking at your monitor displaying a clear image made up of 100s of thousands of individual pixels of light. distance dictates the scale of visibility.

It’s the same way when you watch TV or look at your phone you don’t see each individual pixel of light but the collection of each pixel to make out the image you are looking at.

The light spreads out as it travels through the air. Tiny bits of the light get scattered around when they’re going through the air and they bump into a piece of dust or a water droplet. If you’re looking at a light source from far away almost all of the light is getting scattered away and not making it all the way to your eye. When a bunch of light sources are close together, like in a city, all that scattered light adds up to a general glow. That’s what light pollution is, the scattered light lights up the whole area.

When you are looking at one light from space, the distance means there is no way you can see it. When there are a lot of lights, there is more light bouncing off of the earth and up to space for you to see. You aren’t actually seeing one light, you are looking at a lot of lights that look like one light point. You can’t actually make out one individual light from the whole group you can see. Unless you are using a low earth orbit satellite with a high resolution camera that can really zoom in.

Imagine every light is firing bullets in all directions. But the bullets are incredibly, incredibly thin and narrow.

The bullets ricochet off any reflective or coloured object, losing a little power each time.

If the bullet *hits* your retina in your eye, you see that bullet. If it doesn’t, then you don’t. You don’t SEE the bullet moving, you only see it if it bounces around and ends up hitting your retina.

In a small room, with a bright bulb, there are billions of “bullets” being fired in all directions by the bulb. Most of them don’t hit your retina, but enough do – and from all directions, after multiple ricochets, etc. – that you see everything in the room in front of you (and that only because the retina is behind the hole of your pupil, which faces forward).

As you go up into space, though, the chances of those bullets from that same bulb hitting your eyes are minimal, almost impossible. Maybe one bullet would in a billion. You wouldn’t even be able to tell that one bullet hit, because it’s so tiny compared to when you’re in a room with positively billions of bullets hitting your retina every second. A single bullet probably wouldn’t even register on the most sensitive of sensors.

However, if you take a city’s worth of light, all those stray ricochets off the pavements, street lamps, glass windows, etc., over an entire city… the same chances are present but there’s SO MUCH MORE light to start with that your eye would collect maybe one bullet from one bulb still… but there are a million bulbs in the city. Each giving out billions of bullets. Each of which stands a one in a billion chance of ricocheting into space towards your retina.

So it adds up. And you see maybe a million bullets form the entire city, from a million different light sources. Which looks like a tiny faint glow.

The bullets are called photons.