How come we can see a source of light extremely far away when the source only illuminates the area much closer to it?

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For example, I’m sitting on my front porch which overlooks the town. Miles away I can see streetlights, signs, etc. How does the source project light to my location, yet doesn’t illuminate my location?

Holy moly friends, thanks for the awards and stuff. I didn’t think this question would spark so much interest, lol. I am thoroughly grateful for all your replies.

In: Physics

22 Answers

Anonymous 0 Comments

The light goes away from its source in all directions. North, South, East, West, Up, Down, and every angle in between.

Think about all the light that leaves the source at the same time in all directions as a sphere of light. As the light travels further away from the center that sphere gets bigger. It’s kind of like blowing up a balloon; as the balloon gets bigger and bigger the rubber of the balloon’s surface gets thinner and thinner because the same amount of rubber is surrounding a bigger volume.

Now pretend that the balloon is a special kind of balloon that doesn’t pop so you can keep blowing it up forever. You will still be able to feel the balloon because you can touch its surface, but eventually the rubber will get so thin that it will be hard to see.

It’s like that with light, as the “balloon” of light gets further from the center, there will still be some light that has travelled in a straight line from the source to your eye. Our eyes are very sensitive to light hitting it directly, so the distance the light can be perceived is much much further than the distance that the density of light will be good at illuminating your surroundings.

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