Astronomy is one of the oldest sciences. Astronomers of early civilizations performed methodical observations of the night sky, and astronomical artifacts have been found from much earlier periods. However, the invention of the telescope was required before astronomy was able to develop into a modern science. Historically, astronomy has included disciplines as diverse as astrometry, celestial navigation, observational astronomy, the making of calendars, and even astrology, but professional astronomy is nowadays often considered to be synonymous with astrophysics. Since the 20th century, the field of professional astronomy split into observational and theoretical branches. Observational astronomy is focused on acquiring and analyzing data, mainly using basic principles of physics. Theoretical astronomy is oriented towards the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain the observational results, and observations being used to confirm theoretical results.

Before the 19th century astronomers could learn very little about stars apart from where they were in the sky. But when spectroscopy was invented in the late 19th century, astronomers gained their first tool for analysing the light of stars. They could now learn how stars ‘worked’.

This was the start of astrophysics, but now astrophysics covers much more than stars. It deals with questions such as:

• how do stars and galaxies form and evolve?
• when did the first stars form?
• how are the components of a galaxy, stars, dust, gas and 'dark matter' related to each other?
• what are the different components of the Universe, how much of each is there, and where are they found?