thinly spread gas and dust
Space may seem empty, but actually it contains thinly spread gas and dust, called interstellar medium, that gradually collapses over immense stretches of time and collects into denser clouds of gas and dust. The atoms of gas are mostly hydrogen and are typically about a centimeter apart. The dust is mostly carbon and silicon. In some places, this interstellar medium is collected into particularly dense clouds of gas and dust known as a nebula . A nebula is the birthplace of stars. Our sun was probably born in a nebula around 5 billion years ago.