Astronauts in orbit float because they are continuously falling around the Earth.

The longer version

Orbiting crews appear weightless because the spacecraft and everything inside it are falling toward Earth together. Gravity at that altitude is still strong; what is missing is the sensation of weight, since there is no floor pushing back. Gravity has not been turned off; it is simply unopposed.

Forward speed is the key. A station moves sideways so quickly that as it falls, Earth's surface curves away beneath it, so it keeps missing the ground. This continuous free fall produces the floating effect and explains why objects released inside simply drift alongside the crew. The same principle applies to any object given enough sideways speed.

Where this entry sits

The night sky looks calm, yet almost everything up there is moving, burning, or slowly changing. These facts cover planets, stars, the Moon, gravity, black holes, comets, and the story of how people began exploring beyond Earth. The full list sits on the Space and Sky page, where every entry is listed in order.