Space · Living in space and watching the sky
Light pollution
The sky that disappears over cities
You can see it with your eyes
The numbers
- What it is
- Light sent where it is not neededMostly toward the sky
- What it causes
- A veil that hides the stars
- Who suffers from it
- Astronomy and nature at night
How it happens, step by step
Light goes up
A badly shielded streetlight sends part of its light toward the sky, where there is nothing to light up.
The air spreads it
That light meets the air and the floating dust, and is sent back in every possible direction.
A veil forms
A hazy glow forms above the city, which makes the background of the sky pale instead of black.
The stars vanish
Against that pale background faint stars no longer stand out, and they simply stop being visible.
It can be fixed
Just shield the lamps so they point down: the wasted light stops at once, and the sky comes back.
To get an idea
Light sent upward lights up something that is not there, and falls back like a veil over the city.
It is the only kind of pollution that disappears the instant you stop making it.
Fun facts
These are not in the book: there was no room on paper.
Light at night confuses insects, migrating birds and animals that hunt in the dark.
It also changes the rhythms of many plants, which set their seasons by the length of the night.
It is the only kind of pollution that disappears the instant you stop making it.
A polluted river stays that way for years, while wasted light ends as soon as it is switched off.
Just shielding lamps so they point down sends the light where it is really needed.
A shielded lamp lights the street better, because it does not dazzle the people looking.
Test yourself
The first question is the one printed under the QR code, with the answer the book did not give. The other four only exist here.
Question 1 of 5★ is the one from your book
What is light pollution?
Question 2 of 5
Why do the stars disappear?
Question 3 of 5
Who else suffers from it besides astronomers?
Question 4 of 5
What makes it different from other kinds of pollution?
Question 5 of 5
How can it be fixed?
Riddles
I do not dirty the water and I leave no trash, and yet I steal something from everyone: above many cities I have already erased a milky band that was always there. What am I?
I am made of something useful in itself, but sent to the wrong place: upward, where there is nothing to brighten. What am I?
I am the only one of my kind that disappears the very instant you stop making me. Just turn a lamp to face down. What am I?
Try it yourself
Look at a streetlight on your street: if you can see the bulb from below, part of its light is going upward.
Compare two different streetlights, one shielded and one not: the shielded one lights the street better and dazzles less.
The words
- shielded lamp
- A lamp that sends its light only downward.
Sources: Wikidata (Q214619), Wikipedia (Inquinamento luminoso).