Our Solar System
The Solar System contains the Sun and the objects that orbit it, including eight recognised planets, dwarf planets, moons, asteroids and comets. The inner planets are rocky, while the outer planets are much larger and dominated by gases or volatile materials. The Solar System is part of the Milky Way galaxy.
Stars and galaxies
Stars are enormous objects in which nuclear fusion releases energy. Their colour, temperature, size and lifetime vary. Stars are grouped into galaxies, and the observable universe contains vast numbers of galaxies. Looking farther into space also means looking further back in time because light takes time to travel.
Human exploration
Space exploration has expanded our knowledge through satellites, robotic missions, telescopes and crewed flights. Satellites support communications, navigation and Earth observation, while robotic spacecraft can investigate environments that would be difficult or dangerous for people to visit directly.
A useful way to learn astronomy
Start with the objects closest to home: Earth, the Moon and the Solar System. Once those relationships are familiar, concepts such as stars, galaxies and cosmic distances become easier to place in context. Use quiz explanations to identify terms worth exploring further.