Space, also known as outer space, is the vast expanse that exists beyond Earth and its atmosphere. It is an almost perfect vacuum, with very low density and pressure. Space is not completely empty, it contains a low density of particles, predominantly hydrogenplasma, as well as electromagnetic radiation.
Key Concepts
Universe: The universe is everything that exists, including all matter, energy, planets, stars, galaxies, and the contents of intergalactic space.
Stars:Stars are massive, luminous spheres of plasma held together by gravity. They produce their own light and heat through nuclear fusion reactions in their cores.
Astronomical Units: Astronomical units are used to measure distances in space. One astronomical unit (AU) is the average distance between the Earth and the Sun, approximately 93 million miles (150 million kilometers).