Astronomy
There are two main types of astronomy, observational and theoretical astronomy. Observational astronomy uses telescopes and cameras to observe or look at stars, galaxies and other astronomical objects. Theoretical astronomy explains what we see. It predicts what might happen. Observations show whether the predictions work.  The main work of astronomy is to explain puzzling features of the universe.  For many years the most important issue was the motions of planets. Many other topics are now studied.