In astronomy, the universe is "everything out there". It contains the sun, all the planets including Earth, all of our galaxy, plus many other galaxies, and all of outer space. It's huge - scientists with radio telescopes can only see a tiny part of it. It's so big that distances are measured in light years - the distance light travels in a whole year. To travel in a spaceship, using today's knowledge, to even the nearest star would take centuries. There are more stars than we can count or even see. In between the stars and galaxies it is mostly empty and very cold.

Cosmology is the science studying its origin. Different centuries had different theories about that. Now, the most popular theory is the 'Big Bang'. It tells us the universe was gathered at a small point, and then exploded (Bang) a long time ago