Why can't you open a window in space?

Think of a window in your home. When someone opens it, a soft breeze slips in. You can feel it cool on your cheeks and smell the grass outside.

Astronauts live in a spaceship far above the clouds. Their spaceship has windows too, and through them they can see the stars. So why can't they open a window in space?

Inside the spaceship there is air, just like the air in your room. The astronauts breathe it in and out all day long. You are breathing that same kind of air right now. That air keeps them alive and comfy.

Outside the spaceship, space has no air at all. It is empty, with nothing to breathe. Not even a tiny puff floats out there. Out in space, nobody could take a single breath.

The air inside pushes on the walls and windows all the time. It presses outward, like air squeezed inside a big balloon. Out in empty space, nothing pushes back. What do you think the air would do if a window opened?

Whoosh! The air would rush out through the window, very fast, into empty space. It would zoom away like air from a balloon when you let go of its end. Soon the astronauts would have no air left to breathe.

So the people who build spaceships make every window sealed, which means closed so tight that no air can slip out. They use thick, strong glass that never opens. Each window stays sealed for the whole trip.

The sealed windows keep all the air safe inside. The astronauts can breathe easily. They can still press their noses to the sealed glass and watch the stars.

Space has no air, so the air inside would rush out of an open window. That is why spaceship windows stay sealed.

Behind each sealed window, the air stays snug inside the spaceship. Out beyond the glass, the stars shine on in the empty dark.